I recently made a scarf for a swap which it turns out is hypobolic crochet!! Now I have some understanding of hyperbolic maths though not much but apparently crochet is the best way to model it. In simple terms you start with a line or a point and then each line out form that gets bigger so you end up with a plane that turns in on itself. In scarf terms you get a corkscrew effect which is easy to do and very effective.
Also this last weekend I saw more hypobolic crochet becouse the UK crochet coral reef was at the NEC. It was really fun, i wish i'd gone down to London now to see the American one but I'll have to make do with the photos here instead.
So what about tiny hats? Innocent smoothies run the Big Knit each year, they ask people to knit little hats which then get put on their smoothies and sold in Sainsburies then 50p each smoothie goes to Age Concern. If you look on their blog you will see my friend Heather's hats being showcased too. I plan to do a few this year though I don't think I will be able to match her or indeed the other friend I know is doing them who has done over 30 so far! Oh and when I say knit they are happy to get crochet ones too.