I would tell anyone who would have questions about FZ and Jeff and Vinnie to read "Two Orchestral Stupidities" in Frank Zappa's autobiography. Letting Jeff and Vinnie go was primarily a business conflict over money.
Scott Thunes was by his own admission a very difficult person to work with, so much so that he took himself out of the business. There were several good articles on him a few years back. His bass work with FZ was brilliant.
Jack Bruce was basically hired for the session on Apostrophe, he was not a member of FZ's road band to my knowledge.
FZ hired many musicians who could read very, very well (Vai, Tom Fowler, Bruce Fowler, Chester Thompson, Ralph Humphries, Arthur Barrow, etc.) and also non-readers (Adrian Belew, for example) who brought their own spin to things.
Someone was asking about Jeff Berlin's level of activity in the Music Biz. Like Jimmy M has stated, he has several decades worth of recording work, less so since he moved to Clearwater, but he has lately been touring with Dennis Chambers, Scott Henderson, Larry Coryell and others when he chooses to.
Jeff stated in an interview that he moved to Clearwater and started PSM to care for his son when he had a serious illness. I would have done the same thing (and as a matter of fact chose to stop touring full-time when I did to care for an aging family member). Some things are more important than your gigs.
Here are Arthur Barrow's thoughts about working with FZ:
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Here is Jeff Berlin's Allmusic page that lists some of his credits:
http://www.allmusic.com/artist/jeff-berlin-mn0000237300/credits
I have several albums by Gil Goldstein, Ernie Krivda and others from the late 70s that Jeff played on not listed on the Allmusic page. He had an active career in New York and LA and has started to more actively tour since his sons are grown. We will no doubt hear more from him.
I would encourage anyone who can hear them to go hear Zappa Plays Zappa. It's as close as you will get to the FZ experience these days.