Well this is dumb, lets go over the Smartphone\Tablet market Real Quick, iOS *nix based, Android *nix based, RIM OS 7 *nix based, WebOS *nix based, see the trend here? The only one not *nix based is WP7... This move makes no sense for a platform base.

Nokia will now be dead within 4 years with this choice and I don't think they can repair the damage ever, this is beyond short sightedness. They spent the last couple years pushing QT adoption for development on Symbian and Maemo\Meego for the last year developers have been promised look you develop with QT and your applications will work on Symbian and maemo\meego smart phones as well as any tablets using Meego... Now Meego has been dropped by Nokia, now even if they change there mind a year from now when they see the move to WP7 has not positively effected their smartphone market-share globally or in North America they have no where to turn, even if they moved back to Meego they already killed developer support for QT and the developers are not going to trust that Nokia will stay the course with it so no one will come back.

Here is my BS crystal ball for smartphone Market-Share globally for 2010-2015
OS 2010 2011 2012 2013 2014 2015
Android 33% 35% 38% 39% 40% 40%
iOS 16% 18% 19% 19% 20% 19%
Symbian 31% 22% 14% 11% 9% 8%
Rim 14% 15% 15% 14% 15% 14%
WebOS 1% 3% 5% 7% 8% 11%
WinP 3% 4% 5% 6% 5% 5%
Other 2% 3% 4% 4% 3% 3%