I tried syncing my devices with both a desktop and laptop when I first started with Zune last year. It works, but it can get messy, especially when I tried purchasing music from two computers. Eventually, you can sync it all, but if it gets messy, you may need to restore to one computer or the other. In no case, will you lose anything you've downloaded or purchased from one device or another. I sync with two computers, but I only download with one, or through my devices; and I purchase (with my Zune Pass credits or MS points) only through the one computer. I have not had any complications with this approach. At one point, I was syncing three devices with three computers.
Worst case is that you can log on to MS support chat and they'll get your account and devices in order.