But reading the above, I'm getting worried. Several exchange sites experienced several problems so far, but AFAIK it never ever happened that a site had lost its clients' money!
Really?
bitcoinica - lost funds - still in liquidation/lawsuit - deposits haven't seen a cent.
Crypto-X-Change - losts funds - operators AWOL - depositors haven't seen a cent.
bitfloor - lost funds - still operating - making slow repayment of lost funds (~3% so far IIRC)