Over the weekend, reports have been piling up saying that iPhone syncing with iTunes doesn't work for some users on Windows 7. The official Apple forums have several threads related to the issue, so it's quite safe to assume the issue is real.
Looking for a common denominator, it seems that having a motherboard with an Intel P55 chipset is the key cause, but I personally have a similar issue (iPhone starts syncing, then reports an error) on a laptop with another chipset, with freshly installed Windows 7.
Some of the suggested fixes include using a USB hub or a PCI USB card for connecting your iPhone, and disabling Power Management for each of the USB ROOT HUBs on your computer. But none of these seem to fix the problem for everyone.