I spoted a strange behaviour on fee calculation right now.
I was sending a transaction and it told me that babble about my balance not being enough to include a 0.001 fee that would be necessary to process the transaction.
I lowered the amount to take out that 0.001 so I could pay the fee and when I went to send it it told me that the fee would be 0.0005 instead of the 0.001 stated initially.
So, I went and changed the value of the transaction again to be my complete balance minus the 0.0005 fee. When sending again I got the same popup stating a fee of 0.001 would be needed.
I went back and changed the value to be my complete balance minus the 0.001 fee and sent it and it only charged me the 0.0005 fee leaving me with 0.0005 on my wallet
If one of the devs wish I'll PM him the tx ID. Not posting it here for obvious reasons. This should be mainly related to the client itself and probably has nothing to do with the transaction, but maybe it helps to see what the transaction was.
Using Bitcoin-Qt 0.6.0.6-beta on x64 Ubuntu.