The Odds a Firmware Update Will Relock Your iPhone: Very High

Just a word of caution in case Apple decides to release an iPhone firmware update, say... tomorrow —or next week or whenever: if you have a software-unlocked iPhone, don't update until it gets confirmed that the unlock is not affected. All software unlocks are vulnerable to Apple's firmware updates, say the Dev Team.

As someone from the iPhone Dev Team puts it:

...they [Apple] can beat everything. IPSF or us, it doesn't matter.

Apparently, unless you steal the RSA key, which is a top secret thing and highly improbable, Apple can re-lock all the unlocks with their next firmware update. As the same person said, this could be like the PSP firmware and the war could continue until one of the two parties give up.

Free iPhones of the world, keep your eyes open.