Number of apps that actually look like they're worth having: ehm... the Kindle app's kind of nice, although I never really read on my desktop or laptop. Microsoft's Mahjong and Solitaire. OneNote MX would be nice if it weren't for the huge drawback of being full screen and the fact that I also have the regular desktop OneNote.
In fact, that goes for all of them. With the exception of maybe Remote Desktop (which I usually run full screen anyway), I have seen exactly zero apps so far where the benefits outweigh the drawback of requiring full screen (on a desktop PC). This includes built-in as well as store apps. Calendar and Weather are nice for their start screen tiles, but the apps themselves I rarely use because they're full screen. I'd rather use desktop IE or (even better) Outlook to add things to my Live Calendar which I can then see on the start screen tile.
Media center could be run windowed, and that made more sense as a full screen application than most Metro apps. Hopefully windowed metro apps will be added in Windows 9. Until then they might be nice for a tablet, but utterly pointless on the desktop.