I met Michele Bousquet at Autodesk University 2008 and she was full of energy when it comes to making Revit Content available. She wrote to tell me that its been six months since they kicked their Revit Market off and they have over 2500 families now (they call them "assets").
What I found interesting is that the items in most demand are "entourage"...people etc. The biggest sellers have been furniture, plants and decorative accessories. That makes some sense to me. Do we really want to model that stuff to add to a scene so we can get a better sense of realism?
She also mentioned that the greatest concern expressed by customers/users thus far has been "reliability". It is one thing to download a family for free and see it "break" when you flex it. It is another thing entirely if you are paying for it. She said that their Revit Market has done very well because of their Revit Certified Content process.
I really appreciated the "60's era free-Revit-family" vibe we've had for many years but also recognize that many firms and users are really reluctant to share many hours work so freely anymore. So Turbo Squid is providing a solution, you don't have to "give away" your content anymore and you can download something you can count on with a bit more certainty.
[Edit: Fixed the link > Revit Market]