Has anyone tried this hop on, hop off bus in Paris? My understanding is that you can buy a 1-2 day pass and use it as many times as you want in those days? Is this a good option for getting around? The price is not bad 27 Euro for two days. I was thinking, at least for the first day, using this bus to familiarize myself with Paris with the "grand tour". Any comments?

We think it is a great way to introduce yourself to Paris. The commentary is sometimes hard to understand. And it is a pretty good way to get around to the various sites for the days you are there although the Metro and walking are also very easy once you have your bearings.

I thought a couple of bus routes were also a good way to get a general city orientation. Maybe somebody can give us the number and best places to catch them.

Bus 29 takes you from Bastille to the Gare St-Lazare, passing the Pompidou Center, the Bourse, and the Opéra Garnier along the way.

Bus 69 starts at Bastille and ends at the Champs de Mars (Eiffel Tower), passing the Hôtel de Ville, the Louvre, and les Invalides.

Bus 96 starts at St-Paul and ends at the Gare Montparnasse, passing the Hôtel de Ville, Musée Cluny and the Tour Montparnasse.

Of course, on all of these routes there are lots of other lovely sights as well

Tour busses cluster around Garnier Opera.
The Hop on, hop off busses are mostly for sightseeing, not basic transport. If you only want local trans. to get around, don't waste money on this, just buy pass for subway and busses.