• It just works. Drop your files into a folder and forget about it.
• You can join more than one computer to the same account and the files sync between both computers. eg one at work, one at home.
• If you're away from you computer and you need a file, you can get it from the web interface. (But of course you'd only do this on computers you trust
• There are different levels of privacy. Private files are only seen by you. However you can share files with certain people, by supplying their email addresses. You also have Public files which can be downloaded by anyone at all with the given URL. Much more control than senduit.com for example.
• Photos put in the photo folder are instantly made into galleries. Neat.
• You can roll back to a previous version of a file if you make a mistake.

Having said all that, I wouldn't trust super secret work or personal documents to it, but for keeping a backup of photos and non-sensitive personal docuements, it works a treat.

Also, there's a referral program on at the moment, so if you sign up via the link below, you get an extra 250Mb of space. And so do I as well … go on … its free, and you'll be glad you did.
https://www.getdropbox.com/referrals/NTI3NDkwMDk