Wait...
... so if you get lucky and generate a POS block you lose control over those coins for 520 blocks?
What if I need those coins to pay somebody in the meantime? How fast are PPCoin blocks-- how long would I have to possibly wait?
From the FAQ:
Because stake is withheld from spending for 520 blocks, if you do need to keep your balance around to be spent soon we provided a configuration option 'reservebalance' to help you keep your balance from being used by stake. You can add a line 'reservebalance=10000' to ppcoin.conf and restart your ppcoind. This way ppcoind would try to keep your balance above 10000 coins when generating stakes.