For those who have a Mtgox yubikey and now wish to unlock it and re-program it for other purposes, the unlock codes have been leaked:
http://www.sendspace.com/file/in4ss6

Search for your serial number (as printed on the dongle) in the txt file downloadable at the above link (ignore/delete any obviously dodgy exe files that are downloaded at the same time). And then use the tools from http://www.yubico.com/products/services-software/personalization-tools/use/ to reprogram.

The entry ending in A relates to slot 1, while that ending in B relates to slot 2.

I discovered this via this page: http://crypto.stackexchange.com/questions/14809/any-use-for-now-defunct-mt-gox-yubikey. I have no idea who/how/when this was leaked.

While this list allows the yubikeys to be unlocked and re-programmed, assuming yours is listed (and mine was) - it is not a leak of the stored keys in the device.

If you had funds at MtGox when it eventually died, then obviously you should think about whether you really want to re-program your yubikey - as at some level it allows you to to prove ownership of your account there.