So Mother 1.0.0 Alpha 2 was released today. Quite a lot has been improved but there are some features still to be implemented so there will be an Alpha 3 before the official Beta program starts. Registered Alpha testers can view the change log at www.mugginsoft.com/testing/mother.
The update includes the latest build of Sparkle (1.5b6) which insists upon code signing. I have tested this with a pre-emptive Alpha 3 and it all seems to hang together. So fingers crossed for future updates.