Occasionally I see a Shishio from Samurai X/Rurouni Kenshin , so that is pretty rare, but I think I'm the only person I've known who went as one of Juppongatana - last year I was Yūkyūzan Anji, the fallen monk who teaches Sanosuke the Futae no Kiwami (punch that makes things explode!). I see at least a Kenshin each year, and one or two Sanosuke's as well, so going by that, I suppose that, for being so popular, cosplays from the anime are fairly rare. I don't think I've ever seen any of the female characters at all.
This year it's a slightly more common character - Ginko from Mushishi.