I have used a Dropbox solution similar to the one you mention, and simply drop my dev files into the right location on each machine. This worked great most of the time, but a couple of times there was a connectivity or other issue, and the files didn't get updated on machine #2. As you can imagine, when I started editing on #2 the changes were propagated to #1, overwriting my original updates. Uggh.
Anyway, I finally shelled out the $50 annual fee for a hosting plan on 1and1 (or was it godaddy, or somewhere similar?), which solved most of the problems I was running into. Btw, these plans typically provide git support as well.