It depends on the type of syncing. Things is so barbaric in its wifi syncing, but they're promising a cloud service, but I'm sure that will cost money. Bento should be compatible with your Bento library on your desktop, and depending upon how that's syncing you should be fine to sync that database and Things.
Some apps sync via Dropbox or iCloud, and I think that's what Ashwood11 was getting at in his response. If an app is not updated to make syncing possible, you can't do it.