Yeah, I've noticed it for about a year or so now... especially girls my age. I remember in year seven I wore a Cookie Monster top on one of the sports days, and I was laughed at and given weird looks by girls from my school. And now it's the trend!
It was casual clothes day at school about a semester ago and I saw a girl wear a Kermit top. I complimented on it and asked if she was a muppet fan. She's a nice enough girl, but she gave me this funny, even patronising look and said, "err... yeah, I like them," not sounding very convinced. And then she's like, looking at her top, "the frog is my favourite, y'know... Hermit" (!) It's the same with tops with old-school things on with them (cartoons, bands, etc), they've been really popular lately. There was a chick with a Banana Splits top and I came up and talked to her and she was like, "uhhh... I actually don't know who they are, really...".
I have a lot of Muppet/SS tops though... a couple of months ago I even got a Fraggle Rock hoodie for my birthday!