I have n900 and yesterday i won lumia 800 in a contest. I have tried lumia now for few hous and all i can say: its faster and smoother than n900, but not better for me.

What sucks in lumia 800 is:
-no skype
-no wifi/usb tethering
-no text search in mp3 player
-calculator doesnt have "memory" or list to show
-nokia navigator is bad. I prefer sygic mobile maps 10 in n900
-still no grooveshark app
-no flash
-no fm sender or what the hell it is...
-too low space, only 13gb for pics and music
-no mass memory mode
-no microsd card slot
-no real multitasking
-only micro simcard is accepted
and the list goes on...

Lumia is good for basic use but for me n900 is way better. Even though i hate the slow and unresponsive n900.