The T-Mobile myTouch 3G has been rooted. The wonderful folks of XDA developers have already hacked the myTouch 3G and were even thoughtful enough to provide detailed instructions on how to gain root yourself!
As with all rooting methods, if done incorrectly it may brick your device, so please tread carefully when following the instructions. Rooting a phone can be beneficial to those who want to take advantage of the full power of the phone--you can upload custom ROM, install apps to SD Card, etc--but it comes with obvious danger such as turning your once functional phone into a very expensive paperweight. If you're not the most tech savvy we recommend you sit this one out, but for the rest of you--go right to your rooting needs!