Ok, I've been struggling with mine ever since. Restore did seem to have fixed it up temporarily though.
My ipad is a 64GB 3G. It's on 3.2.1 and jailbroken with jailbreakme.com. I have been restoring it back to 3.2.1 by holding the alt key when clicking restore, and changing the hosts file by adding
74.208.10.249 gs.apple.com
to fool the system into checking with apple that I am restoring it with the latest copy of the OS.
It works fine with just a normal restore, but after jailbreaking it again, and installing ***** REMOVED ***** as well as restoring all the downloaded apps, and then switching on the 3G network, it becomes unstable. Either there is a problem with the jailbreak which makes it unstable and takes it to the initial activation screen with "Connect to itunes" when rebooted, or there is a problem with ***** and installing the other apps, or something is interfering with the network capabilities (3G) and it crashes due to it. I am unable to figure out clearly.
I've gone through this process multiple times now, but there isn't any clear point where the problem starts. And once the problem starts, it doesn't show up every time. At times, I am able to reboot it normally, at times it boots only when connected to the computer.. and at times, it takes many times to be able to boot up..
Any help would be greatly appreciated!