I just upgraded my Dropbox account [referral-free link] from 2 GB to 50 GB; I started using the file synchronization service about a year ago, and since the day I started using it, it's been one of the best pieces of software and Internet services I've ever used.
Neat little upgrade graphic!
There has been zero downtime, their software works flawlessly through proxies, through firewalls, through SOCKS5, etc. (and, of course, through an unprotected connection), and it's always as fast as my connection allows. I rarely give such a complete recommendation for a software product, but Dropbox, like TextMate and Tweetie, is an absolutely indispensable program for my needs.
I use it to sync all my personal files, some application preferences (I often use symlinks in OSX to get the preferences to sync properly), and even private files (to do this securely, I first create a secure disk image in OSX, then mount it, copy files to it, then unmount it. Once unmounted, it will sync the encrypted disk image over Dropbox to my other computers).
The only caveat is that synchronization works great, but not if you have the same file open on two of your computers at the same time. I currently use my Dropbox across 3 Macs and 2 PCs, and there hasn't been an outage on any of the computers.
If you'd like to give me a little extra storage space (not that I need any, but y'know, bigger is better), here's a referral link: Create a Free Dropbox Account.