I read that multiple deposits to paper wallets could render them unusable.
I hope I am wrong.
Some people tend to think you can only use paper wallets once for some reason.
You shouldn't re use a paper wallet after you import it into QT client and SPEND. This is because the QT client sends the change to a new address. So if you assume it went back to the original address, and then deleted the QT wallet you will lose coins.
You can receive an unlimited number of transactions TO a paper wallet. They wouldn't be very useful otherwise. Someone sending you can extra satoshi will do absolutely no harm to a paper wallet. Unless some miner is very generous it is very likely the tx will never confirm anyways and will eventually be dropped by the network.