I try to read everything I see about the iPhone, but I haven't seen anything about problems syncing with PCs. There may be some problems syncing with Outlook or some other MS programs, but I can't imagine the company that sells iPods would have a problem developing a device that couldn't sync with a PC.
Since the iPhone is not scheduled to be released until "late June", it is unlikely that anyone can say for sure how well it will sync with a PC. I agree with ColsTiger though that Apple's experience with the iPod should make this a non-issue. If you are concerned about it, I recommend you hold off purchasing an iPhone for a week or two after it is released. Any issues should be out in the open by then. Or you could always buy a Mac .
Let's also keep in mind--in addition to wot's spot-on comment that it's way early to know what problems iPhone has with the PC--that iPhone syncs to the PC the same way it does to a Mac: via iTunes.
This is a very important point. Apple has taken great strides to make sure the round-trip user experience from device to iTunes is the same on Mac OS and Windows.
From what we've seen in the keynote, syncing an iPhone to your computer (Mac or PC) looks no different than syncing an iPod. I expect by the time June rolls around, any problems won't be platform specific as they might be just pure iPhone related.