As somebody who owns N900, GS, iphone 4 and have used WP7 device for a day and bought Zune HD back in the days, i really like the UI feel of WP. It's the smoothest UI i have ever used.

Though it got 3 big problems to me that are: that tile home screen, i doubt Microsoft is letting big hacking community around it and browser.
While WP multitasking is no Maemo or webos imo they have done better job implementing it to the UI than Symbian, iphone or Android on this new update.
I will certainly at some point own Windows Phone like any other mobile OS, but i have always waited at least for a year with new OS's(other than for N900).