Luckily it’s dead easy to do: enter Preferences (either by opening up Tomboy and clicking Edit -> Preferences, or if you’ve got it on your GNOME panel, right-click the icon) and select the “Synchronization” tab. Choose the “Local Folder” service and find your Dropbox, which is inside your home folder by default. Inside of Dropbox, make a new folder for the Tomboy Notes database, and select that folder.
Dropbox acts like any other directory on your computer, so when Tomboy syncs itself to your Dropbox, Dropbox automatically syncs that database across all the computers you have it installed on. Now you can access your notes anywhere!
As for Zim, syncing is even easier, and gives you more benefits. When you start a new wiki, just remember to save it somewhere in your Dropbox folder – that’s it. If you’ve got a wiki you’ve already started and want that synced instead, you need only move the folder you saved it as (remember, Zim wikis are saved as folders, not files) to your Dropbox. You’ll have to tell Zim where it is next time you start the program, of course.
Beyond file synchronization, saving Zim to your Dropbox has another two little bonuses: if you login to dropbox.com and navigate to the place where you’ve saved a Zim wiki, you’ll find you’ll be able to actually read your Zim notes anywhere, regardless of whether Dropbox is installed or not! Since they’re stored as plaintext, you could also edit them without Dropbox or Zim by downloading and re-uploading the file.
As for the other extra feature, if you’ve worked with wikis at all you probably know most give you the ability to revert changes or view the history of an article. Zim doesn’t come with that functionality – which is understandable, as storing every revision of an article can clutter up a folder right quick. But Dropbox will give you a similar feature:
It is what it looks like, folks. Wiki history, brought to you by Dropbox, accessible from your own file browser.