Does the standard client provides forward anonymity?

[Sergio_Demian_Lerner]

Does the wallet stores the used addresses forever, even if all the coins used by these addresses have been sent to other users?

It would be an interesting property to optionally provide forward anonymity, so if a computer is compromised by an attacker, then the attacker cannot reconstruct the transaction history based on the private keys in the wallet.

Those old private keys should be securely erased from memory and disk.

[Stephen Gornick]

Does the wallet stores the used addresses forever, even if all the coins used by these addresses have been sent to other users?

Yes.

Those old private keys should be securely erased from memory and disk.

The client doesn't know that the address won't be used to receive money againt at some future time.   While address re-use is discouraged, people do it all the time.