I've got a Thunderbolt Display. Its a massive convenience.
It can be used with any graphics card that has a mini-displayport (some ATI cards have them, plus there are dongles to go from full-sized displayport to mini-displayport, but I'm not sure about HDMI/DVI-to-mDP adapters)
When you plug the Thunderbolt display into a mini-displayport of a PC, it acts just like every other screen that is on the market. But NONE of the usbs, mic, camera, ethernet or speakers will work, as they require a Thunderbolt connection.
Hope this helps...
BTW, the Thunderbolt display only has usb2 ports, this may not be an issue with older macs, like mine. But if I had usb3 on my mac, I'd want usb3 on the display too. Maybe sit tight for a couple of months and see what apple has in store for us (should get slimmer and get usb3 at some point, a là iMac)