Are you getting the same error code when you are trying to upgrade your i products?
Ya, me too.
After more than 5 hours download the latest iTunes 10.5 and iOS 5 (Ya, my internet connection speed is only 1 Mbps), it was 6:15am in the morning.
6:18am : As usual, manually backup all the data in my iPhone 3GS before upgrade, just in case. Always play safe!! 
6:30am : Everything seems smooth…. BOOOM!!! Error….
6:56am : After few tries, i have no luck. I try to google it, seems i am not alone.. Hahaha, the problem is occurring because there are too many people trying to access Apple’s servers at the same time.
7:00 am : After restart my Windows PC, there is no any error occured. Yeah!!
7:36 am : It took about 20 minutes to restore my iPhone.
7:37 am : And restoring my iPhone apps is a long wait (it depends on how many apps and size you have in your iPhone). While waiting for the full restore, i can’t wait to try the new OS, the app that I wait for so long – Notification Center & Reminder!! (I knew i wont be able to find Siri in my new OS, because i am not using iPhone 4S). Here is the snap shot:
8:15 am : Now i have no need to use my dumb dumb finger to snap picture on the touch screen, instead of just pressing the volume-up button!!!
8:21 am: ALL DONE!!! There are some small bugs, but do not caused big problem.