Yes. Infection. You're seeing a trend in my gallery. Ponies. PONIES.
I can tell you how it started. It's not just MLP:FIM. It's not just Lauren Faust's work, which has been really amazing. The highest contributing factor is the fact that MLP:FIM is done in Flash. That's what I feel makes the show so special. Flash is Magic. That's how it started.
I'm still relatively new with Illustrator, but I can see how the line work on the animation is done. So I decided to give it a go. Twilight Sparkle was my first Illustrator Test Subject. That turned out pretty well. Then one thing led to another and soon my Illustrator has the likes of Rainbow Dash, Spike, Fluttershy (which I'm still working on, and thus remains unreleased) and today, Applejack and Applebloom.
I'm not calling myself an expert. No. But I'm having a ball with this. And it's great practice. There will be more.