How do I sync snippets across multiple computers? (TextExpander 3, 4)

Use Dropbox to sync your snippets between Macs. Dropbox accounts are free for limited storage amounts -- see www.dropbox.com
Make sure you have Dropbox installed on all of your devices, and logged into the same account. If you have Dropbox for Business, get in touch with support for help.

If you want to sync to iOS devices as well, you'll need to use TextExpander 5 for Mac and the steps here. 

Sync TextExpander 4 or 3

1. On your first Mac, the one with your snippets, open TextExpander to Preferences > Sync and check Dropbox. For an iPhone or iPad go to TextExpander's Settings > Synchronization and set "Use Dropbox" to "On".
2. You will be given an option to "Replace Dropbox Data" or "Link to Dropbox", you want to choose Replace. Once you do, if you look in your Dropbox folder, you should see this file appear: Dropbox > TextExpander > Settings.textexpander.
3. On your second Mac, go to TextExpander's Preferences > Sync and check Dropbox. For an iPhone or iPad go to TextExpander's Settings > Synchronization and set Use Dropbox to On.
4. Select the option to Link to Dropbox Data. Any subsequent devices you setup, or later times you turn Dropbox on, always choose Link.

Troubleshooting Sync 

If you have trouble, try turning Dropbox off then back on.

Turn Dropbox sync Off:

1. On your Mac open TextExpander to Preferences > Sync and set Sync preference to None. On an iPhone or iPad go to TextExpander's Settings > Synchronization and set Use Dropbox to Off.

Turn Dropbox sync On :

1. Go to TextExpander's Preferences > Sync and check Dropbox. 
2. Select the option to Link to Dropbox Data.