I know this question has already been answered, but... Typing "lsof" (stands for: list of open files) in a terminal prompt will give you a list of all open files and the name of the process that has them open. Use the kill command with the process number to kill whatever process has the files open you want closed. Afterwards you should be able to unmount the disk.

If you're technically savy, you can try to completely disassemble (everything except the display) and clean and dry each part along the way. I've heard there are good guides here (ifixit) for that, but I found a 200 page pdf on demonoid as a torrent. I spilled an entire 20oz glass of water on my keyboard while it was powered on. I did this this weekend and was quite surprised how well my mac is working afterwards. Also... On your system, I believe there are immersion detection sensors under the black keyboard seal (behind the logic board/optical drive), that will tell you if your warranty is void. If the stickers are white (not red) and you have applecare you might be able to get apple to fix it. Be really careful though, as I've heard opening up your system beyond taking out memory voids your warranty. Hope this helps. Good luck.