For those concerned about the security of storing your information online Spider Oak is a service worth considering. Their zero-knowledge policy ensure that—by design—they cannot access the data you store on their servers. Your data is encrypted on your computer and then sent to their servers (they don't have access to your private key).

Benefits:

• Securely store your data online, and have it sync between computers.
• Allows you to select which folders to backup/sync.
• Less expensive then Dropbox. Really great student rates.
• Allows over 100 GB. This allows me to use it as an offsite backup for all my files (except video).

Downsides:

• Not as user friendly. UI needs some work.
• Sharing options well behind Dropbox.
• No apps/services integrate with it.
• Upload process seems slower, though I haven't actually tested this.

Given the downsides, I use Spider Oak for backup and sync exclusively while also using a free 2 GB Dropbox account to take advantage of all it's awesomeness.