Today, as we're sure you're aware of, the untethered jailbreak for iOS 5.0.1 was released. Tools like RedSn0w and packages like Corona were released to take advantage of pod2g's untethered exploit.
If you've had an iPhone 4 since launch, then it's entirely possible that you've preserved your baseband up until now for unlocking and resale value.
If your primary concern is preserving your baseband for an UltraSn0w unlock, then you'll be happy to hear that PwnageTool is back, and it packs full iOS 5.0.1 compatibility in tow...