All in, I would say that I had a positive experience since opening the box. The unit is well-made, albeit, lacks a 'solid' feel. This seems to be the direction that Nokia is heading in (e.g. Nokia 6220 Classic).
As a long-time Nokia user (my last phone being the E51) as well as an Enterprise-biased user, I was pleasantly surprised to find the phone supporting Nokia's Mail for Exchange client. An added bonus was that the virtual/soft T9 keypad was natural to use, with just enough haptic feedback to give it feel without being overwhelming.
Music
3GB of music took over an hour to copy over using Windows Media Player 11's sync capabilities, which I found something concerning, especially since this is supposed to support USB2.0. Music playback is amazing over the stereo speakers on the left side of the device, and I found stereo widening to be more natural over the speakers than the headset. Playback quality was comparable to, if not slightly better than my iPod Photo, although I did find that there was a volume setting that was too soft, and bumping it up a notch made it a tad too loud.
Video
I had a bunch of MP4 videos downloaded from YouTube that I copied onto the device. Some played back fine, others did not fare as well. I have some videos that I previously converted from DVD rips using the Nokia Internet Tablet Video Converter (available from Nokia Beta Labs) that I use for my Nokia N800 Internet Tablet. I will load these up later and share my impressions of the playback. I did, however, notice that the Dark Knight trailer that was included on the device was playing back in a stretched format, and sadly, this does not show off the true capability of the 5800 as a video player. The tips & tricks videos work fine, showing what how good a properly formatted/converted video can look on the 5800. As my set is an EU model, Chinese characters are not displayed, making it impossible for me to use this with my Chinese/Japanese pop titles. Interestingly enough, my G1 has no problems with Asian character sets
Performance
In most instances, there is a slightly noticeable lag in making a selection and moving back to the previous menu. The lag is especially bad when starting or ending video/music playback, but I'm just being picky. There isn't much lag when composing SMS and emails, so that's good in my books.
Connectitvity
Haven't tried connecting via BT yet, but microUSB seems to be much faster if I set the device as a Mass Storage Device than as a Music device. I'm not impressed with the microUSB, which is about as handy as the extUSB standard created by HTC (I have a G1 as well) -- I do wish they stuck with miniUSB as this now means that I have yet another USB cable that I need to tote around when I travel.
Contacts Bar
A nice idea, but not something I am accustomed to yet. The amount of data displayed is just enough to show the last 4 interactions/communications, which is almost pointless. It would help if they incorporated Chat/Conversations as they did in the E51, but this remains to be seen.
Going online
Setting up my APN and Wifi connections were a breeze, although the new OS deviates slightly from the previous incarnations of S60. Connections are now classified by Internet, and you simply add the relevant profiles into the group and order them by priority, and the system simply gets you online according to the preferred connection.
Web browsing is pretty good, and very much consistent with the typical S60 browser. I have not experienced anything out of the ordinary yet. Compared the web browser on the G1, this one is almost primitive. I managed to get Mail for Exchange working, and as expected, it worked perfectly and quickly. All my appointments, tasks, emails (over 70) and contacts (over 500) were synced in a matter of minutes. I have not yet set up my personal Gmail, but I do not expect it to come close to the Gmail push mail client on the G1.
Camera
Tried this indoors last night and was properly disappointed. I get better pictures off my Sony Ericsson K800i, a pretty dated model with a 3.2MP camera and no benefit of the Carl Zeiss optics found on the 5800. Whether there is improvement in natural light remains to be seen. That said, the camera on the 5800 is a huge improvement over the G1's.
UI consistency
Nokia needs to get their act together on this one as the UI lacks implementation consistency
e.g. in the web browser, you drag the page around as you would on an iPhone or G1, but in other parts of the system like the menus, it works conversely
e.g. some apps require a double tap to execute, others will run the file with just 1 tap. I suspect there may be more to this, and will be looking into this in the next 24 hours.
Impressions
The 5800 remains first and foremost a phone, media player second. The lag can be somewhat bothersome for a device that is touted to be a media device. So far, I'm having mixed feelings about the 5800 - I love it as a phone, and was easily texting and calling friends and family within minutes (zero learning curve), but I hate the lag and the UI quirkiness.
I've also noticed that the screen is not a transflective TFT, i.e. it washes out in daylight and the screen is barely readable.
Agree with his thoughts on the 5800? Eager to get one? Well, let us know YOUR opinions either here, or at the forum!
The nokia 5800 mobile phone was already relevealed by Nokia partners in Qatar.
I cant beleve it! 
:!: 
... any one activated it ?? uptillnow nothing happened 
... finally i won 