After reading the disturbing tale of 25,000 stolen BTC ( http://forum.bitcoin.org/index.php?topic=16457.0
), I have decided now is the time to make 100% sure my data (including bitcoins) are secure.
So here are my suggestions on how to secure your stuff. I am not security expert, so input is appreciated.
Assume your computer is compromised. Get a new, uncompromised computer with a safe internet connection (where you can be sure no one is changing your unencrypted internet data). On the new computer, create a new encrypted password file using a password manager like KeePass with a long, complicated password. This is the only password, besides the user password to your computer, that you will have to memorize. In your password manager, create new, unique, complicated passwords for every single account you have. Do not bother memorizing any of these passwords... that is what the password manager is for.
Next, assume all data stored on disk will eventually be compromised by someone. Thus, use tools like encfs or truecrypt to encrypt all data on disk. For each encrypted volume, use a different password, saved in your password manager.
For bitcoins, transfer all bitcoins out of your old wallets into new wallets. Otherwise, the money can be stolen at any time if someone has the old unencrypted wallets. Make sure the new wallets are never written to disk unencrypted; they should only ever existed on disk in encrypted form.
If you have private/public key pairs, you will need new ones.
Only place encrypted data into data storage tools like Dropbox, wuala, or tarsnap. Personally, I wouldn't ever trust a data storage service that they encrypt your data. Assume your data is compromised, and encrypt it before using their services.
You have no choice but to assume your computer is not compromised during daily use, or your passwords, and thus all your data, will be stolen. If you ever suspect that your computer has been compromised, then follow the procedure listed here. Change all passwords, rencrypted all data, and create new data (bitcoin wallets and private keys) if necessary.