This is an excellent article covering how to get those lost files back.
It happened with me when I upgraded my hard drives and one of the older ones using ReiserFS just lost all the data that was on it while I was copying it to the new drive. Not deleted, no hard drive failure, it just vanished! (I heard some other people having the same experience with ReiserFS so I moved on over to Ext3...)
This would have helped allot getting the 100+ Gb of data back, so have a read here and bookmark this site, you will need it sooner or later!
How to recover lost files after you accidentally wipe your hard drive