Again, I dig up this comment text because I would've loved to know it before I found out myself. Unison can function as a free DropBox very easily (actually the parts that SparkleShare doesn't cover and vice versa):
I wanted to change stuff on pc1, then change stuff on pc 2 and pc 3 and have it all merged and pushed out to all the computers.
Unison can do this in a star-topology (all machines sync+merge to a central machine), and it works fantastic. You get versioning-backup of the files as well, something that was rather nice now that my Lucid-computer crashed because of the Intel GPU-bug and destroyed my full HomeBank file.
It works like a backup, I have all my files synced to all my computers and the server.
I've written a small script that uses incron to check for new/changed files, and cron to periodically just do a update. It also uses notify, to notify about stuff. Just needs a small nice indicator-applet and it's golden ;-)