I had this emailed this morning and I thought it was worth investigating as I haven't read much more so don't take my word for it. Looks legit.
Blacksn0w RC2 Unlock for iPhone 3.1.3 05.11.07 Baseband Released in Cydia March 28th, 2010
Steve the guy who was behind PushFix 2.0 (the first real fix for Push Notifications) for unlocked iPhones has just released Blacksn0w RC2. This version of blacksn0w is basically a repackaged version of the original unlock released by geohot, which this was not. This was released by MSFT Guy.
1) Only installs if you are really running 3.1.2 or 3.1.3
2) Checks your baseband version only installs if 05.11.07
3) Properly backs up and restores your configuration if uninstalled
It fixes all of the WiFi problems, and eliminates the "infinite Apple boot loop" for the 3G[s] that updated to 3.1.3 through PwnageTool/sn0wbreeze. It wa a small percentage, but it still existed for some.