Seems to be happening to me daily now, and is very annoying. Is this iOS 4 related? Never had this problem before. This is on my 3GS.
Yeah Apple is punishing you for not getting an iPhone 4 lol Try going into the settings and then Safari clear the cache, cookies and history then reboot. Then once you boot back up login to your forums and see what happens. If it persists you may need to reload the OS.