It seems odd that Apple are looking for feedback from only a small select 'invitation only' group..... why don't they try to gain as much information from their customers as possible. They could save time and money by just trawling through all the threads on the MacRumors forum !!
People here are not so good at testing. Just read the threads. Some guy says "works for me" without stating what he does with his computer". Another guy says "printer is broke" without saying what steps he did to try and resolve the issue. These are absolutely useless as test reports
The best testers are people who are good at resolving and narrowing down problems. They will be able to write up the minimum number of steps needed to re-produce the problem and then list the fixes they tried. I write software, and believe me those kinds of reports are 1,000 time more useful that what you typically hear. Most complaints turn out to be users not understanding the software.
Good bug reports help the user too. If I get a very specific bug report and the log files and input data are included I can see what's going on and fix it in 20 minutes. and the user is very happy. But "it's broke" type reports pretty much have to go on the bottom on the pile and that user will have to wait until the problem effects someone else who can better describe it.