I've had a couple of "plays" with zenfolio. The nice thing is you can open up another zenfolio account if you like to try again.
Things I really liked.
The structure system to organizing images.
The image quality.
The UI, and the ability to switch to "viewer" mode.
It is possible to set up custom sales, ie effectively using the zenfolio interface as a web agent.
Things that it needs to be my choice:
The ability to place personal html code within the text areas. I know that zenfolio provides buttons to do this which on the surface of it makes it very easy, but not customizable (as smugmug) for a more "html" confident user.
Things that would be nice.
Comments could be useful.
A bit more personalization of the "skins."
I guess watch their space, but with smugmug offering a lot of these things already, albeit with a more complex and limited gallery organizational interface, the balance for me is still with smugmug.