If you need to access your DEVONthink Pro Office database from multiple locations, the iDisk is a perfect place for it. First make sure to switch your iDisk to sync mode (System Preferences > .mac > iDisk sync) and enable ‘automatic’ synchronization. This let your Mac(s) keep a local copy of the iDisk’s content for much higher performance. Copy your database to, e.g., the Documents folder on your iDisk and use it from there.
You now only have to make to keep the real iDisk synchronized to your local copy. While the Finder does this automatically in certain intervals, it’s definitely advisable to also trigger synchronization manually before you leave your Mac. In the Finder, click the double arrows next to the iDisk’s name in the side bar to start the synchronization and don’t log out or switch off before the Finder is done. You can find more about the iDisk and iDisk sync’ing in the online help of System Preferences.