Been poking at my brand-new Nokia N900 all evening and here are some first impressions and opinions. They are completely from my own viewpoint. I should mention here that I have used Linux a lot and even purchased the very first Maemo-device, the Nokia 770 when it came out so I'm not a total stranger to these devices. When comparing to other devices I will, however, be comparing it to my second generation iPod Touch (doesn't have the faster processor of the iPhone 3GS) and phones in general.
I'll come back with more thoughts when I have had some more time with it and try to empathize with other users than myself :).
The Hardware
The N900 is built like a brick. Both in a positive and negative sense mind you. It weights enough to feel both solid and expensive but also just enough that it makes you wonder if its too much to carry in your pocket. Since its pretty much a rounded brick/square by shape too it looks (and feels) bigger than the current iPhone even if it's not much thicker, the tapering edges of the iPhone makes a lot of sense. This device has clearly been designed by engineers. It's a functional design and there's not much more to say about that really. The iPhone design is clearly cooler but it doesn't have to make room for the physical keyboard.
The N900 uses a mini-USB-connector for charging, just as most phones in the EU, at least, will in the future and that's great - less cables and more people who have the same type of charger.
The screen, oh boy, the screen. Its SHARP, it has a very high DPI and very readable at least in-doors like I've used it now. You can fit a lot of information on it and if you have normal eyesight you can surf most well-designed web-pages without zooming and tapping around, you'll want to zoom in on the main text if it's longer though. At this point I should say something about the touch-technology. The iPhone and iPod Touch uses a capacitive screen which is very cool because while it requires a real finger touching but when it does, it can distinguish between several fingers and you don't have to press very hard. The N900 has a resistive screen which doesn't require a finger - any reasonably sharp object will do - but it can only distinguish from one point. It also requires some pressure to be able to recognize the interaction. This means that the N900 touch-interface is indeed not as good as the iPhone's - but it does have some positive features, it is more accurate and it becomes even more accurate when you use a stylus and you can click around with your fingernail for better control than a full finger (the iPhone won't recognize a fingernail at all until the finger itself touches). Since I've used pen-based systems before it feels nice to have that choice. The N900 screen is very sensitive so the poking doesn't have to be very hard either.
I should mention that the screen, out of the box, is slightly sticky until you have used it for a while - probably something gets left on the screen from the screen protector. Not a big deal but it is annoying if you are used to a smooth out of the box experience.
The physical keyboard is great to have, It was a very important part of why I wanted the N900, but I haven't had enough time with it yet to say if I like it, I like it more than the iPhone's smaller, vertical, virtual keyboard and I like the fact that while typing you can actually see the whole screen instead of having a sliver of space where you see your last sentence.
The Software
First of all, you need to know that the N900 multitasks, for real. You can run many programs at the same time, which is great when you are waiting for something to happen or just want to check up on something in another browser window. I used my iPod touch for all my communication on our last vacation and as much as I love many of the applications, It drives me nuts that they are actually restarting every time I change them and often reloading a page when I switch to it - which is doubly annoying if you are on a slightly slower 3G-connection.
The N900 is definitely a browser-phone, the browser is very, very, good. It uses a Mobile version of Firefox that is very comparable to the desktop version. You can use plugins like AdBlock and others. It has Flash-support so you can use random flash-based websites such as
http://www.bambuser.com instead of waiting for a special application. Basically its fast and full-featured so instead of using special little interface-applications like on the iPhone, you can actually use the browser like it was meant to.
It is also the first phone that really lives up to the "Mobile Computer"-name in my opinion. You really don't need to connect it to anything, other than the Internet, to do what you want to do. You get full access to the filesystem as well as a terminal window for those of us who like typing commands and using text-based tools. I haven't tried it yet but you should be able to install most of the Debian/ARM software on the phone which means you can run a web server on it or really program on it.
That said, the additional software available currently is not very impressive, there are more Maemo-software available for the earlier versions of Maemo but since the N900 is the first Maemo 5 device and I'm among the first to receive it, most developers of the older software haven't gotten around to make the necessary changes. I must also admit that I have my reservations about Maemo-developers competing on design and polish with the iPhone-developers. Make no mistake, Linux/OSS-developers create very interesting and powerful software but they seem to lose interest when the interesting technical challenges have been done. I hope I will be proven wrong though!
Last point about the software-side of things that is just plain awesome compared to iPhone/iPod - it has enough power, and multiple codecs, to play divx/xvid-videos out of the box. You can just drag and drop Movies or TV-episodes onto it (it acts as a USB Storage Device when connected to a computer) and watch them without transcoding or any of that tedious stuff that stops me from actually watching anything on my iPod touch.
Conclusion
No conclusion yet. :). Ask away for more details, I'll be writing more soon! In general I'm guardedly positive about it, I like it and I want to like it but the competition on the smartphone market is currently very fierce and that is great for us consumers!