Thanks as always to @sidd, we now know what steps to follow to register the latest version, 2.6.7b2...

-> Open the Control Panel for Snitch.
-> Hold down the Option (Alt) key and click on the "Purchase" button. If you hold down any more keys than just Option, it won't work.
-> A tiny window with only two fields will appear. Enter any registration info you want in them. Just don't leave both blank, else it won't work.