Do the museum or church passes (for many different
sites) work well and are they worth it? Do you still have to stand in line, or can you bypass the ticket line if you have a pass?
You can by pass ticket lines with a pass or reservation if required. But the line for the security screen can be just as bad.
Note that most churches are free, unless you want to visit specific areas (bell towers, crypts, etc.). If the church has been turned into a museum, there will be an entrance fee. Many churches have limited hours of operation for tourists, and ask that people not tour the church during services (although I did witness a baptism at the baptistry in Ravenna).
For your museum and Vaporetto passes in Venice go to: http://www.veniceconnected.com/ Pick up the passes at the airport, train station or Piazza Roma booths. For your museum passes in Florence go to: http://en.uffizi-com.waf.it/museo_dett/27-state-museums/3175-uffizi-tickets-reservation.html No if you present these passes at the door you won't have to wait in a long line. They usually will send you to another ticket booth to pick up your actual entry ticket. You have to understand that other people buy the same passes you buy. So at times you might have to wait in a short line. Usually the long lines are to buy the tickets, to wait in line, to get in. Most churches are free. But you might have to wait in another line. Depending on how popular the church is, will depend if there is a line.
You've been to Disney World have you? No they're not that bad.
You can also look at the Firenze card in Florence. It is good for almost every museum, public transportation, etc. It is the first season in use and it won't even appear in the RS guidebook until the 2012 addition. No line of note anywhere and I was there in the summer. http://www.firenzecard.it/?lang=en There is no pass that really makes sense in Venice.
I feel cheated, they didn't have that card last year. They had some stupid museum pass that didn't have any decent entrance hours. As to Venice, YEAH, I think that's the best for now.