Does Bitcoin wallet encryption also protect my sending and receiving addresses?
Clearly your receiving addresses, your sending addresses and their associated aliases are readily available without the passphrase to your wallet as they are visible upon opening the Bitcoin client without entering the passphrase. 

It's perhaps also worth noting that even if your wallet is encrypted, a successful attacker who has a copy of your wallet could install a keystroke logger to obtain your passphrase. 

This would seem more likely to happen when your computer is compromised through installing a trojan etc than if someone physically found say a lost notebook PC (for which the attacker would need to install the keystroke-logging software &amp; remote access software, and then give you your computer back so you would type in the passphrase next time you wanted to send coins!)

Sorry, I don't know where the sending and receiving address descriptions are stored, so I don't know how to protect them - hopefully someone else can answer that.