Bits gleaned from the DVD background chatter, where I'm almost
sure at least half the people in the room were sober:

Premiere

The storybook sequence which opens the series originally ran long and had to be trimmed down. (It was also rendered via painting.) Running past allotted run time is a problem for the series in general and the actresses claim their main booth order is 'Act faster!'

Canterlot is visually inspired by Minas Tirith. (It's also literally that shining city on a hill.)

Some of the backgrounds started as being more complicated, but got simplified because it was just hard to pick out the action against all the detail. The show's color palette also works against the artists at times -- bright ponies, bright backgrounds, bright objects... And as-is, the series is pushing the limits of what Flash can pull off. (In particular, the manes of Celestia, Luna, and Nightmare Moon were hell to animate. Nicole Oliver (Celestia) claims her own hair just does that naturally.) There's still some cheating going on, particularly with character mane and tail positions. But it gives for what it takes away -- it's easier to do multiplane depth and there's no color bleeds.

Color-coded magic auras were a late idea: up until that point, it was difficult to tell what was affecting an object and, if there were multiple unicorns on site, impossible to tell who. They don't appear around everything targeted until well into the season.

Spike's voice actress (Cathy Weseluck) thought of him as being very baby-young at the start and later mentally added a few years, explaining the vocal evolution in the first season.

The extended Apple clan was going to be even larger than shown, but suffered the same problem as reusing G1 character names: Hasbro couldn't establish the trademarks.

Tara Strong (Twilight) often records in a separate studio (and city).

The use of "everypony" and other such wording wasn't in the first scripts, and a lot of time went into searching for all of the other wording to make sure it was gone.

Threat levels faced by the characters are a constant concern: there has to be enough so that there's real stakes, but it can't be so scary as to alienate the kids. The tightrope sways... and given that the series does have a Nightmare Fuel page on TVTropes, occasionally goes over.

It takes about five weeks to storyboard an episode, three weeks for layouts, and another three weeks to animate. Revisions add to that. A lot.

"There's no wrong way to be a girl."

Winter Wrap-Up

Pony advertising and signs are pictogram based to make marketing the show into other countries easier, plus images register faster to the brain than words.

The songs stick in the staff's heads, too. (There were about eight variations on the chorus.)

Twilight originally had a different design: light blue stripe in her hair and a small moon for a cutie mark.

Pinkie Pie's voice is basically Andrea Libman pushing herself to the limits of loud, fast, and crazy, added to a game of 'What sounds can I make?'. (She goes as fast as she can, they play it back, and if no one can understand what happened, take two.) So if those limits had been any higher... And yes, her natural voice is at the high end. At one point during the final commentary, she goes into Pinkie Pie out of nowhere and you can hear the entire room jump.

There was in fact a debate as to why saddles and bridles would exist in a world without anything that rides.

The bird flocks near the end of the episode are a Flash glitch recruited into a special effect. And Twilight's coordinator outfit is magicked on to keep it from having to go over her head...

"We thought the snow should be white."

Suited For Success

Rarity's glasses are an Edith Prickley homage.

The original series manual for Rarity suggested she should sound something like Audrey Hepburn, so that's part of where Tabitha St. Germain drew the voice: make the diction very clear, then add Dutch, English, then some Connecticut to keep it at least a little North American, and go for the posh.

Why do scissors have finger grips? No one knows... Possibly the same reason slippers are front hooves only, although in that case, Rarity was not in a mental state to be watching all details of her outfit.

The song everyone in the fanbase thought was a secret hidden assault on network meddling with shows and having to keep clients happy? Was a secret hidden assault on network meddling with shows and having to keep clients happy. Daniel Ingram was practically daring anyone to send him a note... So call one for the viewers: a Take That sailing under the radar -- until it hit the air.

Discussion of timing the music against the animation makes voice actresses heads hurt.

The basic pony design is simple -- but apparently it's really hard to do freehand: mess up the proportions even a little and the entire thing falls apart. Convention embarrassments seem to have occurred.

Use of visible outlines are generally limited to characters to increase contrast and visibility.

"That's the beauty of Flash: we can actually zoom right inside someone's soul!" And yet concepts like 'rotating stage' make the animation team cry.

The Show Stoppers

Second most common voice direction: "That's just weird."

Third: "That's a choice..."

The actresses who voice the CMC (Michelle Creber: Applebloom. Madeline Peters: Scootaloo. Claire Corlett: Sweetie Belle) were actually age-appropriate for the roles: nine and ten during the original recordings. Dawson Casting averted.

Horsepower on that scooter: something under one.

Scootaloo's mane has a single pink pixel floating in the air behind it. Good luck finding the thing. Better luck thinking of a reason to look.

Tabitha: "Why does the rest of my family not have the same accent?" (And the creative team has no idea where Scootaloo's parents are either.)

The head-piano-repeat is a tribute to Sesame Street.

They're aware that if they even joke about 'Someone should make', someone will. I can feel them itching to abuse it.

Madeline Peters has perfect pitch and a strong singing voice: it made her physically ill to do the end number badly. And thus the audience got to share her pains.

Design style for said bad end number: every bad Eighties musical cliche which ever existed and never should have. And then they asked Daniel Ingrim to anti-autotune it... It's hard to do bad well on purpose. Unless you're Donald Trump, and then it's your whole life, except that you're not aware of it...

The Best Night Ever

As with Suited For Success, it's a whole lot of men designing a whole lot of dresses. The ladies complimented them on the results.

The mice-horse section (pre-credits) was used as a test for hiring storyboard artists.

Yes, they know about the Flash glitch which produced the cyclops pony. No word on why no one stopped it.

Acknowledgement that Equestria is essentially a matriarchy. As if there were any doubts.

The big musical number on this one left a trail of bodies. It wasn't just animating all the ponies, it was animating ponies in evening wear. The joke was that the purpose behind the song was to break the art director, and if they didn't get him, they got everyone around him: new ponies, backgrounds, outfits, musical instruments... haul the corpse away and hire another intern. There's also a forty-person chorus singing in the background -- but they worked for free.

"Fluttershy's descent into madness."

The naming of all the background ponies amuses them. (Hi, Octavia!) And there's a Carl Sagan pony lurking about the Gala, which some people seem to have missed... Also, there's a Craig McCracken (Lauren Faust's husband) character ponified: look for the hat.

"It's such a sweet band: tuba, harp, and double bass." And so they were limited to those instruments (plus the piano) for the Pony Pokey.

The original temp score for the destruction of the Gala? House Of Pain.

And finally, the smashing of the slipper: "I don't need no stinking prince!"