I find the guides very useful but he doesn't seem to be popular on this forum. Why is that?

His description/interpretation of the paintings in the Uffizi is excellent. He's not an art critic, of course, but I think that's an advantage for the average traveler like me. He describes the art in layman's terms.

The museums move things around so much, that it makes me wonder if Mona Winks is worth spending the money on. How often is this book updated?

According to the Rick Steves web site, this book no longer has its catchy title. The listing of his guidebooks there says it's now called: " Best European City Walks & Museums."

If you have a limited time to visit a museum, I think his tours are pretty good for giving you the highlights in an entertaining style.

I'm quite sure he doesn't write them himself -- it's obvious that he has someone who knows something about art giving him the key information, and he probably adds the attitude. I think they're exceptionally good if you are traveling with adolescents. I have friends who got their teenagers through museums by having them act as "tour guide" reading out of the Rick Steves book.

Any book which gives one a greater appreciation of art works could hardly be a waste.