Developer Preview 8 and Public Beta 3 are out.
http://www.cultofmac.com/295984/os-x-yosemite-preview-8-seeded-developers/
http://www.cultofmac.com/295984/os-x-yosemite-preview-8-seeded-developers/
Except... I'm looking for bugs, not doing unpaid QA work. As you said, the beta testing is there to find obscure bugs and spot regressions in features/integration. Something as basic as being unable to add media to a media player (...which is, y'know, pretty important in a media player) is something Apple's QA department is supposed to find. This isn't some sort of super-volatile nightly alpha version.