I anticipate possibly buying museum passes in London, Paris and Rome.
The Museum Pass in Paris, for example, is 45 Euro for a 4-day pass.
Does this mean that I can use the pass for a museum multiple times
during those four days or does it mean I can use it only once (and not
again) at the same site?

The "Roma Pass" (20 Euro for a 3-day pass) specifically states that
you can only use the pass for free admission to the first two museums
visited so it is rather limited. But the Paris "Museum Pass" and the
"London Pass" don't seem to be explicit about this. Do they punch
such cards when you visit a museum in these places or just Rome?

Also, we're in Venice for only two nights and it does not seem worth
it to me to buy a Venice Card. We anticipate only having to pay to go
into the Doge's Palace and perhaps a gondola ride. Is this safe for
us to assume or are there museums in Venice that can't be missed?

Lastly, I purchased tickets on-line for the Uffizi Gallery but it
seems like the Galleria dell'Accademia, the Medici Chapel and the
Bargello are also important to book on-line because the tickets seem
to be selling out in the morning (August 2008) for all of these
galleries.

http://www.b-ticket.com/b%2Dticket/uffizi/

Thanks -- you guys have been extremely helpful in planning my vacation.