All I can offer is empathy. If you read some of my posts, you'll find that Pr's reliablity is spotty for me. I will say it works more than it doesn't, but I can't detect a cause and effect yet for why it stops working. So, I share your frustration. A quit and relaunch fixes many problems, a reboot is required for others. Audio instabilities are often fixed by changing the Audio Harware settings to something else, and back again.
I have worked with FCP7 for three years, and MC for as long as it's existed. I have all three NLEs, and I start and finish most of my projects in Pr, even though I'd grade both FCP and MC as "more reliable." For some projects, it makes more sense to start in FCP. It's more reliable for shuttling. It's timeline markers are better implimented. And of course, it can be used to ingest and transcode to ProRes, which I prefer many times to working with native Long-GOP material in Pr.
Thanks for your reply. CS4 worked great. (except for horiz. scrolling, which I LOVE in CS5.5)
Some additonal info.
I am guessing that it has something to do with the complex AE compositions that it has linked into Pr. Seems like it is bogged down when I make a change in AE. After letting Pr sit for a while, it catches up. But looking at the activity monitor you wouldn't think it was doing anything!
Also, when the problem occurs even trying to play an audio file from the project bin does nothing but change the play to a stop button. It's getting the command but not executing correctly.