For those of you who still haven’t upgraded to iOS4, you might want to save your iPhone’s ECID SHSH on Cydia’s Apple signature server. What this allows you to do is to be able to downgrade back to 3.1.2 or 3.1.3 because Apple has a new security mechanism, meaning if you don’t do this, you won’t be able to jailbreak your iPhone. (given that you haven’t jailbroke it ever)
You never know when you need to jailbreak it so just start pointing your DNS for gs.apple.com to 188.8.131.52.
You can do this by adding the following line to your HOSTS file. For Windows, it’s C:\windows\system32\drivers\etc\hosts
Basically what you are now doing is connecting to Saurik’s Cydia Signature server, which will save your current ECID SHSH for your iPhone’s current OS. (whether that’s iOS4 or 3.1.3 or 3.1.2)
That way, later on you can revert/downgrade!