Please note: This article has been contributed by a user.
This is a "how to" to keep Things in sync between Macs using Dropbox.
mkdir -p ~/Dropbox/Library
cd ~/Library/Application\ Support/Cultured\ Code
mv Things ~/Dropbox/Library/Things, OR:
rm -rf Things
ln -s ~/Dropbox/Library/Things Things
Based off the longer version on my article: Synchronising Things using Dropbox
Note: This sync solution seems to work fine if you don't run both Things apps at the same time. However, the one caveat is that scheduled todo's based on iCal calendars (such as the Birthdays calendar) do not sync correctly. One Things app will have the correct calendar reference, but the other will have a ?. This is possibly because Things uses an internal reference for the calendars, not their display name.
iCal Note: Syncing todo's with iCal calendars and using DropBox (or USB stick, iDisk, or shared network device) will result in sync problems! When using the same Things database on multiple Macs, syncing with iCal may lead to problems!