I just got my bitcoin client working on my thumbdrive in a truly portable fashion, i.e. so that the windows bitcoin client wouldn't put the wallet.dat onto whatever windoze machine that I was using at the time, and then the windoze machine that I was using at work today had a hiccup of some kind while I had the bitcoin client open and my entire thumbdrive was corrupted. 69 BTC, gone.
Don't forget to back up your wallet.dat files, particularly if you use untrustworthy operating systems.
Shit happens...
Although this one may be actually not-windows "fault", perhaps just broken usb pen itself. As others said, boot up some linux livecd like "RIP linux" or even Ubuntu install cd in livecd mode,
copy blocks to image file and try to recover it.