Are you Crazy? Don't jailbreak your iphone 4 immediately! Wait until it's out of warranty. You're playing with $1000 bucks. Who in their right mind would jailbreak?
I depends how important it is. If there is heaps of stuff that you want badly but can't get and you don't take the thing very many places it might get damaged then you should. Though if it would only be a slight convenience then you should wait until the warrant is up