Here's my problem free upgrade story. I upgraded to clean iOS 4.0 and never had a problem (on a iPT 3G). Then i JBed with jailbreakme.com, still no problems. Clean 4.0 installs seem to be OK. I've heard that 4.01, 4.02, 4.1 are not so good-- it's best to be on 4.0. Thats my 2 cents.