My house is 100 years old. They weren't thinking about mounting Solar Panels on the roof when they decided on the direction of the face. We do, however, have a good chunk of land.
On the bigger picture, I think that there could be a heck of a market for pole mounted systems because they are so easy to install (relatively), and thus much cheaper than a major roof job. Also, I know that there are many houses that do not have ideal roofs for a solar installation, and for some, the pole mounted option would be the right solution.
They are also nicely scaleable, as you could add more as long as you have the land and the inverter capacity.
I'd want to not skimp on panels, though. The most efficient per unit area would be the way to go.
EDIT: I think another advantage of these where possible would be due to the fact that rooftop systems collect heat, which lower the panel efficiency, whereas these wouldn't have that problem. For the rooftop systems it looks like cogeneration is in order, where the panels generate electricity and a solar thermal system removes heat in order to heat the home, or water, etc.