I'm 100% sure that i understood what you're trying to do, so please correct me if I'm making wrong assumptions here. I think there is currently no dropbox client for the N900, so syncing via dropbox is not possible. It is possible to send the tomboy notes to the N900 using for example scp or rsync. While doing this Conboy should not run. I'm currently adding support to sync Conboy to the web (e.g. Ubuntu One or Snowy). Then you could sync Tomboy with Conboy via one of those web services. At the moment there are still too many bugs, but as soon as they are fixed, this should be the best solution.