I have an iPhone 3GS, 3.1.2 I jailbroke it myself, easy as to do. I see that there is the new spirit jailbreak out now and it is for 3.1.3
At the moment my iPhone is running sweet as, no problems at all.
What I want to know is what is the advantage of upgrading?
I know that I would need to update my itunes to v9.