Yesterday I posted about a jailbreak for iOS 4.1. At the time, I hadn't done it (was midway through updating to 4.1) but now I've gotten things up and running. Some users are reporting that apps are missing or that they only appear as white icons after jailbreaking; I didn't experience this. If you do, however, try rebooting your phone.
The jailbreak itself hasn't caused me any problems. I've had no randome reboots, or freezes, or random bugs; jailbreak apps (ones found in Cydia) are a different story. Many of my favorite apps are not yet supported for 4.1. biteSMS and FolderEnhancer are two of the most useful apps I used in 4.0.1 but sadly, they are not iOS 4.1 ready. If you are a user who enjoys using many Cydia apps, I'd wait a few more weeks before updating to 4.1 to give devs some extra time to catch up.