yes there is a jailbreak greenposi0n or redsn0w, pwnage tools or sn0wbreeze if you see the benefit upgrade to 4.3.3 if your happy with 4.2.1 wait. then you can play with all those boot logo's they keep adding. 🙄
No need to update at the moment unless you have to. If you were on 4.0/4.1 I would. I would just sit tight and wait for iOS5 unless there's app that requires 4.3.3 which i highly doubt...