Hi, i had same problem after useing iTunes in paralel with LazyPanda install daemon !!! My phone went into endless loop of restarting after white apple logo ... and itunes didn't even detected it anymore.

Problem can be solved by simply starting redsnow ... go into DFU mode ( real restore mode ... not that crap in iTunes ). Problem is ... apple changed trick to enter into DFU mode in 3.0.1 ... correct step is :

1) Connect iphone to PC
2) Turn it OFF ( by holding POWER and HOME together more than 6 sec )
3) Start Redsnow and read instruction or do :
( press POWER and HOME ... screen goes ON keep holding 5-6 sec when screen goes black release POWER still holding HOME ... hold HOME for 10-28 sec )

4) After than redsnow will detect DFU mode and start restore procedure
5) You could disconnect phone before redsnow start to fill it with cracking code and then close redsnow, open iTunes ( now it will see phone and want to restore it ) do fresh restore with UNMODIFIED 3.0.1 firmware ( actualy same version that phone already is )

6) When you finish iTunes restore and phone turn ON in locked state ... do not unlock with SIM or put SIM card into it ... just start redsnow again and folow redsnow procedure one more time for DFU and JAILBREAK procedure ( SELECT ONLY CYDIA not ICY .

7) You have jailbroken and working iPhone ... now turn ON Wi-Fi and in Cydia do complete upgrade.

8) Powerdown phone ( RED SLIDER - hold power for more than 6 sec )
9) PowedUP phone ... connect to Wi-Fi start Cydia ... add ultrasnow repo in source - edit -add ... search for ultrasn0w install ultrasn0w ... restart phone ... put SIM card ...and you should have working phone again

I hope i've helped you :-)