My brand new 05 didn't get good fuel economy. Most brand new cars don't. After a short break in period, the economy improves. In Motortrend tests, this car got like 34 mpg. The Prius did not fare much better- if at all. When you drive the cars like that, you will get that sort of fuel economy.
The problem is people. We don't understand all the aspects of what we're talking about. I run into the same thing at work with engineers. They scratched their heads for days trying to figure out why some breakers were constantly tripping on a temporary cooling tower platform this past summer. They had us run all sorts of tests day in and day out, always with similar answers. Finally when we got tired of it, one of us dumb electricians told the engineer: You know, that power supply panel is out in the sunlight and its about 120F ambient temp out here, that's what's causing it to trip, not something wrong with the equipment.
The obvious missed point here: hybrids and especially plug-in hybrids weigh about 25% more than their engine only counterparts. This is going to reduce your fuel economy in town regardless of whether you're running on battery power or not. It's also going to make braking more of an issue.
I like the C-Max, and I'd get a plug-in version if I got one. It fits my wife's typical route best. We're still waiting. When I see things like this, I get giddy though, because I know resale values will go down, and the car will be more affordable to someone like me who understands that you don't get maximum fuel economy off the showroom floor.