i bite my nails, unfortunately, but i guess that isn't odd. i'm trying to get out of it also
i can be quite OCD too, in a way that it irks me if something isn't in its right 'place' (e.g a lampshade isn't straight, the curtain it sticking out etc). it's not extreme though, a colleage of mine would get freaked out if you moved his pens (his blue/black ones on that side <, his red ones on that side >, and their lids had to be facing inwards toward each other like ><), or if you asked him for a piece of chewing gum he'd be like 'well... will you have 2?' (would only remove them 2 at a time so there was always an even number). That got quite funny, if you insisted that you only wanted one 
i like to meticulously plan things, and order things. i like being given a lot of 'something' to do and figuring out a way to make it easy to sort through. i guess that might be kind've odd.
edit: not sure if it counts as a habit as such but it is particularly irritating (to myself, and others too probably).. my attention-span can be ridiculously low, and I can't help it. the worst is when someone asks me a question and sometimes I'll be replying and then stop in the middle of my sentence and say 'sorry, what was I saying?', cause my brain had thought too far ahead. ;@