As a guy who has been caught up in this fandom for two years now I think I'm qualified to enlighten you all as to what's going on:
First, My Little Pony, Friendship is Magic is NOT the hideous show of the '80s and '90s. It is an amazingly good show.
Second, this isn't a gay thing, it's a nerd thing. The central character is a nerd who gets sent to a small town to learn about friendship.
Third, the fandom is amazing. I have a hard time keeping up with the flood of art, music and videos that they create. there is also a great deal of charity activity.
Links:
Bronies raise over $70,000 for 11 year old suicide surviver.