The Paris Combopass supposedly combines the Paris museum pass and a an inclusive bus, metro and RER pass. Anyone used it? Is it worth it?
It does combine both.
Probably not worth it. You can walk all of Paris. Longest hike (exclusive of Montmartre) would probably be Notre Dame to Eiffel Tower and that's only about two and a half miles (maybe three if you walk along the river).
Think hard about the museum pass as well. I've heard of only a few people who have found it financially advantageous, but it is handy for butting in line.
I've never used either in a good many trips.
IMO, the combopass is not a good deal because the Paris Visite pass, which covers transportation, is overpriced. You'll do better making separate purchases: a museum pass plus either another kind of transportation pass or a carnet of ten single tickets.
For a list of all your transportation ticket and pass choices with links to detailed information about each one, go here.