I think there's a pretty reasonable explanation for how it took off so fast, honestly. Over the past 10 years or so it seems that the average kids' show is getting lower and lower in quality and production values. I know that most shows today suck compared to the ones I watched as a kid (the new Blues Clues pales in comparison to the original, for instance). So when a new My Little Pony cartoon came out, I'd guess most people had really low expectations and looked at it mostly as a source for exploitable images. When I first heard about the hype, I thought it was going to be one of those serioux bizness "so bad it's good" shows. So I watched it and was pleasantly surprised to see that it was actually genuinely well thought-out!

Now multiply this by a couple hundred trolls who have fond memories of Powerpuff Girls and a handful of furries who have a crush on one of the main characters, and you've got an internet phenomenon.