A couple of things:
I think that part of the seemingly slow sales of the Flex can be attributed to its perception as being a large, gas hungry vehicle. Now, we all know that its actual EPA numbers are competitive for the class, but a lot of people never get that far. I can see people who aren't really into cars but need something for their families passing up the Flex just because at first glance it's big, boxy and kind of SUV like. When you go to a dealer with something smallish and economical in mind, the Flex looks too much like the SUV lots of these people are trading in to get them to seriously consider it. I'll bet some people are assuming it's just another SUV and moving on. Consider that the Edge is selling quite well, doesn't get much better mileage, but has a much more "crossover like" profile. It just SEEMS more modern and efficient at a glance.
I also think with lots of Taurus X's sitting around with cash on the hood, many people are looking at the Flex, then looking at the Taurus X for 10K less and deciding they can do without the fridge. When the Taurus X inventory is gone, much of that volume will likely go to the Flex.
Another thing I can't help but notice is once again, the complete lack of advertising for the Flex. What I thought was going to be a media blitz is a barely noticeable whimper, at least in my area. About the only national ad I've seen for the Flex is highly stylized and shows heavily treated footage, or maybe even CGI footage, of the Flex driving around a CGI city. It's pure image and style and tells you next to nothing about the vehicle. My father, a happy 500 owner, recently joked that he thinks the Ford Taurus is a myth, since he never sees any ads for it. Let's hope Ford figured out that you have to actually tell people about a vehicle for them to buy it. I know they're going for the hip thirtysomething crowd and don't want babies and dogs in their Flex ads, but is it too much to ask to have someone get into the second row seat and say "Look at all this &^#%@ room!" on camera? Ok, or something like that...
Anyway, I think it's a great vehicle, but the timing is proving to be unfortunate.