According to different sources, the Golden Master of Mac OS X 10.8 has been submitted to developers. I installed it yesterday and apparently everything is working fine, founding no bugs at all in my daily work with the computer.
In previous developers versions of Mountain Lion, I could find some buts preventing from adequately restoring disk images on flash drives. But this seems to have been ironed out.
All in all, this seems a very solid update to OS X, although I still think that the loss of the Activity panel in Safari is a step backward, not forward.