I'm using encfs to encrypt files in dropbox -- and it turns out that I'm not the only one. In fact, I'm a late-comer to this apparently.
I've just installed Windows on physical hardware for the first time in a couple of years -- I figured I should learn more about this experimental, unstable OS that a lot of people have been talking about. I hear that it's not even based on linux, and that their leader isn't Torvalds (it's some guy called Gates, apparently). It looks pretty slick actually, but their software management model leaves a lot to desired (you have to use your browser to download software and there's no way of keeping track of security updates for anything other than the core OS). I also haven't figure out how to switch to any of the other virtual desktops/workspaces.
Whatever. The FOSS connection lies in the use of Dokan and encfs4win.
Anyway, to get encfs up and running on Windows, go to http://dokan-dev.net/wp-content/uploads/DokanInstall_0.6.0.exe and install
Then go to http://members.ferrara.linux.it/freddy77/encfs.html and download encfs.zip
I dragged the entire encfs4win folder to Program Files. Start encfsw. A notification icon (shaped like a key) should show up in the task tray. Left-click on it, select Preferences and set to Launch at Startup.
To mount an existing encrypted directory, or to create a new one, left-click, select Open/Create and follow the instructions. Simple.