Quick plug here if you guys don't mind: our security product nCryptedCloud protect at-rest data in your dropbox account. Should you ever loose your laptop and want to make those dropbox files not readable on that device, all you have to do is remotely revoke the access key (from the device). Without access privilege, the data is useless. It's free for personal use. Let me know if you guys have any question or comments.

-V.