I have to say I'm really not in touch with children's programming these days. But usually when some shit does come along that seems to be a cultural craze--like Spongebob--I tend to think it's terrible.
What I do think is interesting though, regarding this Brony situation and the backlash that many of the adult male fans are getting, is that if these guys said they were really into Lady and the Tramp or The Little Mermaid they would perhaps get a raised eyebrow at worst. Granted, those things are perhaps not EXACTLY comparable to a show like My Little Pony, but it's in the same ballpark, i.e. animation for kids that is largely targeted toward the female demographic.