It's possible to login in the Mt Gox website and check your balance.
Has anybody tried already? has the website been hacked?
I did.
It didn't accept a wrong password but it accepted the correct one.
The displayed balance was correct. (However, it was also correct in the leaked database.)
It showed BTC, EUR, USD balances (these are the only currencies I ever used, USD have been [and still is] zero days before the shutdown, EUR was 0.001, BTC was ~8) nothing else.
So, unless you are worried that their current database doesn't have correct records of you, you gain nothing by checking it.
My last trade (EUR->BTC) happened ~10 hours before the shutdown and it's still valid now.