Perhaps Nokia is being smarter than anyone's giving them credit for.
1) They're getting a large wedge of cash from MS, which will presumably pay for the development of the more advanced hardware that WP7 needs.
2) They pay a per handset license for WP7, not a huge up front development cost. If the market is lukewarm to them, or MS don't improve the OS enough, they don't lose much.
3) They've promised "disruptive technologies" (which everyone seems to have forgotten). Suppose that's Qt on Android and iOS, in addition to present and forthcoming Symbian/MeeGo units? That would change the whole game. It would also explain why they've divested only the commercial/licensing arm of Qt, while retaining its ownership, developers and roadmap, and are continuing to develop it for Symbian, while also revamping its UI (its only actual weakness).
It could well be that the whole MS "desperate gamble" is actually a win-win. If the W7 handsets sell, they win. If they don't, they have a competitive Symbian (hell, do some Apple marketing and call it "CuteOS" - all that matters is that it runs Qt under and atop a sexy UI) with an industry-wide programming API that they own, competitive hardware that MS effectively paid them to develop, and legendary Nokia build quality.
If such a thing pans out, Nokia could end up doing to MS, in the mobile space, what everyone thinks MS is planning to do to Nokia.
I'd quite like to see that.