My uneducated opinion, and that of a fellow forum junkie, is that the Ultras don't really justify themselves in terms of cost, features and performance, and so forth, just to shave a modest amount of weight off. For an extra pound or two, you get a lot, both in dollar range and capability.
If you have a specific need between a tablet and a netbook, I suppose. But otherwise it seems unwise. But then, they were excluded from my matrix early on, so I haven't researched them to be sure.