I guess several 100k BTC are lost forever.
I remember this story:
"In July 2011, the operator of Bitomat, the third largest bitcoin exchange, announced that he lost access to his wallet.dat file with about 17,000 bitcoins (roughly equivalent to 220,000 USD at that time). He announced that he would sell the service for the missing amount, aiming to use funds from the sale to refund his customers."
Taken from:
http://en.wikipedia.org/wiki/Bitcoin