We seem to have the better results when there are a limited number of official beta testers testing development builds, once we determine a development build is stable we then release a beta to registered users, and then finally as a public release for everyone.
The quality and stablity of development builds is way too uncertain to allow everyone to use them and most people seem to have problems keeping up to date.
If you would like to become a beta tester you can always ask to join. We're constantly removing inactive beta testers to make room for new ones.
See this thread for more info