William Bradford, one of the animators for FiM, runs a small sketch blog. It's a pretty basic entry, but still neat to read through it and check out the different animation stages.
One of his quotes says it best:
"I don't think i've ever been on a flash show that allowed us to push the expressions and posing for maximum appeal: Most of the credit being owed to Lauren Faust's permission, All the former Ed Edd n Eddy storyboard artists, and the fantastic character and set builders."This defenitely shows. I think the facial expressions in this show are some of the greatest I have ever seen in animation, and the big draw for me personally. Everything from the deadpan Twilight Sparkle expressions to Pinkie Pie's off the wall shapes that she pulls off...it's just so well done.
You can find the blog here!