I think I might be one of the few Windows Phone users here, so I might as well post my experiences.
I bought a Lumia 800 a few weeks ago, the price was right (250?), and it was time to upgrade from my old phone (Nokia 5230). I don't upgrade my phones to follow trends. Usually my upgrade period is around 4-5 years
So I am stuck with this phone for another 5 years probably, and I am not 100% sure I mind. Also please note that I am a good "average" user for the phone, and I probably have not found all the ins and outs of the device yet.
The phone is really nice to handle, the touchscreen is good (coming from a 5230 this is no surprise...). The tiles are nice, and the way things work smoothly. I like the camera, the 720p capture, and the the whole phone has a quality feel to it. None of the buttons feel shoddy. Not bad for sub 300? phone. The city view is nice, and a cool app. Plenty of decent apps out, and most of them are actually quite well made, but nowhere near Android or iPhone amounts. Fun Nokia stuff, such as the Nokia Xpress browser, and various other software such as navigational maps for free).
Now to the issues:
The Nokia:
-Battery life is woeful - this is not a big problem, but coming from my 5230 which lasted a week on standby, a 2 day battery life feels a bit short. I know, this is the same with every smartphone these days.
-The charger is also USB port. - This is not a problem either, but the cover for the port is a little fiddly. Charging is thus a little too fiddly, when compared to the 5230 or my old 7110 which had docking station capability.
-The 5230 had a better Navigation app. More options, whilst in this one you cannot set key features such as routing options. Not to mention it is missing key data, such as some speed limits, which were in the older version.
-No memory slots. 16GB is what you get.
The operating system Windows Phone 7.5 & Windows stuff:
-The phone has 7 buttons (including the ones below the touchscreen), and one of them is wasted on the search button. I don't want Bing as my default browser, I don't like it that when I accidentally touch the blasted thing, it opens Bing. This is frustrating when you are watching something on Netflix or taking a picture.
-Windows Live Account is frustrating. I understand it might help you find your phone if it is stolen (though I doubt it), but it is a faf to register on live. Not to mention the initial Live account is hardwired to the phone, so you need to reset the entire thing if you want to change. Not cool.
-No Flash support. This is not a small problem, and God knows why Micro$oft has decided to not support flash on the Internet Explorer browser. Really frustrating.
-You cannot save message drafts.
-You cannot have a ringtone which is longer than 40s and larger than 1MB. The idea is good that you won't have insanely long ringing tones, but I want to have my own ringtone, without the need to fiddle around in Audacity. Not exactly "personalising" your phone.
-No custom user modes. In my old Symbian, you had profiles which you selected based on wanted features. Outdoor, silent, offline etc etc. Not here. This was a great feature, as you didn't have to use the volume control buttons that much.
-Car usage is not as good as with the 5230. In the 5230, you could answer the phone by swiping your finger across. Or decline call by swiping it the other way. Brilliantly easy. Here, you have to swipe up, and press a button. The button is roughly the size of the first joint on my index finger. Not easy to hit if you are not looking.
-The phone does not work as mass-storage device. I don't want to even go into how frustrating this is, due to the next point.
-The phone needz Zune to move music, pictures and videos. This wouldn't be a problem, if Zune were any good. But it isn't.
?Zune does not allow you to transfer any other files, than the above mentioned
?Zune does not support some key features. I have never thought I would miss the Nokia Suite for my 5230. You could save your messages. Send messages from your PC, through your phone. You could upgrade software. None of these are Zune features...
?Zune does not let you go into your phone file system. This is not a problem, but seeing as you cannot do it any other way, you will end up with files which are essentially corrupt. Fun times trying to open some pdf content when you get error messages like "File path not found".
-File sharing through SkyDrive is limited. The phone does not upload the good quality pictures, but instead uploads thumbnails. This is frustrating, because you HAVE to plug it in to get your pictures through Zune
-No counter, to calculate your usage. Fixed by Nokia, who provide a counter.
-No way to share contacts. Fixed by Nokia, who provide an app.
-No built-in photo editor. Fixed by Nokia, who provide an app. (though it's still not really good).
-No multi-tasking. Meaning you cannot record a video while using satnav.
And the biggest problem for me personally: NO OUTLOOK CONNECTIVITY. NokiaSuite used to sync my contacts and calendar with my computer. You can still sync your outlook if you use your Live account, to which the phone syncs. Fortunately you can also sync with Google account. This is however irritating, as it means you need to have an internet connection to update your calendar. Also the phone has no week view by default, and the different coloured tasks now require different calendars.
So to sum it up, most good things about this phone are Nokia. Most issues are Windows related, and in my opinion Microsoft rushed this one a bit too much. They have taken no lessons from the old operating systems, and just hashed something together. The connectivity is the worst, essential and basic features such as mass storage, photo syncing to SkyDrive, and Outlook sync through USB/Wifi are clearly not considered. I was expecting a Windows Phone to work better with Windows. Ah well, waiting for the 7.8 we can wait and see.
I really hope they will fix the issues, or create apps. I don't regret buying the phone though, as it seems to be good compared to other phones in the 250? pricerange, and I want a decent camera in my phone. The sad thing is, this could have been a really nice phone if the software wasn't this bad. Now it's just a nice phone (maybe even better than the 7110
)