An update from someone who was in Paris last week - decided to go to the Rodin museum on short notice one afternoon, there was no line to get in.
Decided to go to the Orsay on short notice one afternoon, again no line. The Rodin was medium full, Orsay was packed. Which isn't a problem on the lower level since it's so open and airy, but when you get upstairs, well it's sardine time. So beware.
If I had been in a planning mood, I would have bought tickets beforehand at FNAC. There's a big one in Montparnasse, and scattered throughout town. It's like a Best Buy combined with a Borders and they sell tickets for everything. But as noted, no need. Also note that Rick indicated that you can get a Rodin/Orsay combo ticket to save some money, that is no longer the case.
Turns out the Orsay has two eating options, one is more sitdown and the other more casual. We ate at the casual one which is upstairs at the roof level and it was very tasty and speedy. Plus, and this is a BIG plus, they had iced tea! Real black unsweetened iced tea, in a glass, with ice! The' glace'! I live for this stuff so excuse my excitement but it was a lovely bonus.