The two big contenders I could find are Ubuntu One and Dropbox.

Both allow me to map a drive and seamlessly sync my files just by copying them in there. I don't need to worry about regularly running a "sync" command. Just drag, drop, done.

Quick Comparison

There Can Be Only One

I really really wanted to go with Ubuntu One. It's cheaper and the money I pay for it would support my favourite Linux distribution. For US$90 I could get 60GB and feel good about paying for Linux.

But it's not to be. Dropbox wins on three counts.

Mobile

Firstly, Dropbox Mobile is supported on a wide range of phones. Sure, I only use Android now, but I may move back to BlackBerry. Bizarrely, Ubuntu One Mobile only works for syncing music and contacts. So, no pictures, documents, movies. Far too limited for me.

Command Line

Secondly, command line options. I run a headless server at home which is primarily used for storing the household's music, movies, and photos. It runs Xebian - a Debian variant. Yet it seems that Ubuntu One only works on Ubuntu machines. While I kind of understand the logic behind that - it's a business limiting decision. By contrast, Dropbox works fine on the command line of just about any Linux distro.

I never run Windows or Mac. But, I'm sure one day a job will mandate that I do - so it makes sense to go with the one with wider support.

Security

Both services use SSL to encrypt during transmission - but Dropbox uses Amazon S3 to keep the contents of the files secure. While I'm sure Amazon has its problems, Ubuntu One doesn't keep its files encrypted and makes no mention of physical security.

Other Options

I'm aware that I could buy several gigs of space via a cloud server somewhere and treat my filesystem as a giant SVN. But this has an easy to use front end, paid support, and apps for my mobiles.

That said, if you can convince me there's a better option - please let me know!

You can sign up to Dropbox using my referral link - that way, we both get extra space.