I recently took the plunge and installed the beta version of iPhone OS 3.0.
I found that my battery life took a MASSIVE hit. It was depleted within around 8 hours.
So I downgraded back to 2.2.1 but it didn’t role back the baseband. Battery life was still bad.
I found out about an app called Fuzzy Baseband Downgrader in Cydia.
Once i had jailbreaked my phone I downloaded it in cydia.
Now all is good and battery life back to normal.