Make damn sure you follow this post if you have not flashed a 3.xx rom before
http://forum.ppcgeeks.com/showthread.php?t=24979
If you are not using alltel, make sure you reset before the customizations go though.
After flashing, please hard reset your phone. This will help prevent issues people are reporting.
If your gps is not working, make sure your location settings are not set to e911 only