Hooking into the signup function

Is it possible to get the singup function to create some extra feilds when a user registers?

i know it possible to just create/update usermeta info with update_usermeta() at any time but i would like to keep things neat in the db and at least create some extras feilds at the same time as the user sign’s up.

I wish to do this via hook/filters tho 🙂