I am having the same problems. I tried to upgrade my Iphone 4 to 4.3.5 on my laptop and the update hung for several hours. I finally disconnected and reconnected and got a message that I had to restore the iphone. This kept hanging too, tried for about 3 days. Finally went back to an old computer and restored the phone. For a while, I seemed to be able to sync partially if I started itunes whilst holding shift and ctrl at the same time. However, now when I sync with my current laptop, it keeps giving me a sync error ("cannot be synced an error occurred whilst writing to the device", occasionally it says "error 14" or error "50"). So at the minute i cannot sync at all. Have trawled the internet for a solution, with some ideas but nothing definitive.
Stupidly (yesterday in a brief period of optimism when I thought everything was sorted), I tried to upgrade my wife's ipad to 4.3.5 - same result. The ipad is now stuck and needs a restore, however i had never synced it with my old PC so am completely stuck.
I have tried removing itunes and reinstalling, that didn't help. At my wits end. Haven't told my wife about the ipad problem yet...that could prove tough - she loves that thing more than me and the kids!!!!
Can anyone out there help?