Totally agree though. I'm not going to pay for a TB of storage until I can moves files I don't need on my SSD anymore (ie RAW photos I've developed) into Dropbox and have them removed from my computer seamlessly.
Sooooo easy to implement, just upload the file. When it's done, run an md5 on the local and the cloud, if same then delete local.
Best part of it is that UI changes done on one system remain consistent when using other machines. Completely took the pain out of a format/reinstall, too.
Trying to constrain Home to my Dropbox folder also reawakened an old skill: Space discipline. With drive space exploding and SSDs still being relatively constrained, I had forgotten how much crap I tended to hoard and not sort through until I was feeling pinched again thanks to my Dropbox quota.
Each of my machines is configured (almost) exactly the same, and all the media/projects/work is available on all my computers at the same time.
I also experience the forced "space discipline" and would add that I also have to have a better organizational structure in general. I'm constantly "re-balancing the tree" that is my directory structure, re-defining and re-grouping my media into ever finer groups in an effort to stop things from accumulating in digital "junk drawers".
On a different note, I disagree with the suggestion of having a "virtual filesystem" that is the entire Dropbox service. I feel that doesn't fit with what Dropbox is: a folder that syncs. I don't want to have to worry about the physical location of my files, which I most definitely would have to do based on my internet speed (which is as good as it can get right now).
That said, don't put your irc client in there... I wind up forgetting it's connected when I leave work only to get tons of notifications at home...
I also have Time Machine backups of both systems.