I have an N950. And even though I was just as sad as everyone when I heard the news that Meego would be discontinued. I can only give credit to the Lumia 800 which I got as a gift from Nokia.
There is a world of difference in smoothness when I compared my N950 and the Lumia 800 which I never thought possible and it's in favor of the Lumia 800.
Also the social integration which I was so fond of on my N900 is equally well or better (if the bugs get worked out) implemented on WP Mango.

My n9, from expansys, actually shipped from Marseilles, so there are definitely n9s in France .

When looking for a certain function on the Lumia I always find myself stumbling around without much clue, trying to guess the contents of the cut-off metro labels, until I find the function I was looking for, or until I give up.
Really, WP is so very unintuitive it's no longer funny.
There's no multitasking either.

Emmmm
no there is

Ha ha! I mean multitasking, not a multitasking simulation with screenshots and freezing/killing apps in the background.
Just look at the different clock times on the screenshots. No multitasking, sorry.

Unfortunately I wasn't able to test my Lumia too much - its out of service 50% of the time on two of three networks I've tested and when it has signal - it tops at 2 bars where N900 and N950 get constantly 5. Does someone has similar experiences or just my unit is faulty? On top I don't like Metro and the crippled browser, good thing is that my wife is not that picky

I dont see a world of difference in smoothness. They run equally as well. Considering how much more Maemo 6 is doing, I'd pick the N9 any day. I hate all of the use of back buttons used in WP7. I got lost easily trying to create an Xbox avatar, ended up losing my changes. Then there's the times I want to go back and then crap! There goes the web page I was just looking at because I hit the browser back instead of the system back. I dumped my lumia back to the wife too, they're going to have a huge female userbase. On the plus side, the N900 is back in my hands

My personal review...
"The Good":
- Fast boot times
Note that it cheats; if you try to run any application right after boot it will show "Loading...". Even considering that, boot time is still around half that of the N950.
This is actually more useful that it sounds. It means that when the N950 and the Lumia are both off and I need to look something up, I turn the Lumia on.
- Universal home and back buttons that work.

"The Bad":
- Unstable
I've seen it hang on boot (repeteadly), hang while installing an application, hang while uninstalling an application, hang while upgrading to the newest release, fail to automatically check mail (for an entire weekend!)
- Total and utter lack of multitasking
Even the LOCKSCREEN is considered "another application" and if you lock the screen you lose your current minesweeper game. Try this, it's not an exaggeration, I'm completely serious.
Of course additionally the usual complains about not being able to load webpages in the background, to download files in the background, to wait for PDFs to render in the background....
But Maemo is the only mobile platform left that does multitasking right (and ironically, Windows Mobile <= 6.5), so I guess everyone is already used to this crap.
- Non discoverable UI
A relative of mine was not able to play music using the builtin Zune application because after launching it ("tapping on "Music&Videos") you get a screen with "Applications: YouTube" and nothing more. Not even a single hint that the application is a panorama and that you should scroll right to see the actual music and videos.
This relative eventually rejected the device and returned it to me.
- Poor battery life
Being less useful than a decade-old Palm handheld, one would at least expect astronomical battery life. But for some reason it is actually worse than the battery life on my N950....
- Useless volume control
It is already way too loud at minimum volume (1/30). I am yet to listen to music at more than 5/30 because I fear I will break the speakers. And you cannot set independent alarms / music volumes.
- Horrible audio quality
Not a WP7 problem I guess. But my Lumia sounds horribly worse than my N950. It always sounds distorted; maybe related to the above problem.

That's just pathetic. The more I hear about this sad excuse of an OS the less impressed I am. But then maybe I'm spoilt.

As good an example of "form over function" as I've ever heard. They're clearly trying so hard to be cool that they're crapping their pants - and all the user is left with is a faint whiff of ****. Simple never goes out of fashion!