This is for the newcomer or those hearing about other phones.
I write this in support for the developers of the N900 and Maemo, and in support of all those who own an N900.

1) Why N900 ? Other phones are more cool (or so they say)
Well, other phones might be cool, but N900 is among the very best - hardware wise, and also software wise. Cool factor is varying according to those you hang out with, I guess. N900 is for über-tweekers and freedom fighters alike - 99% is open source and you may even get directly in touch with the guys making the stuff - how cool is that ? I claim that it gives all users of N900 an edge

2) What to do with the N900 ?
Whatever you like - I personally use it for almost anything, I can think of - camera, video streaming(recording), remote control for my stereo (actually a pc hooked up with an amplifier and an infra red receiver). I use the GPS in my car for navigation and listen to songs on my (outdated) car stereo via the fm-transmitter. I work part-time as surveyor -and I use the GPS recording facilities when I don't have the need or the time to bring out the heavier high-precision GPS (Leica). I use various tools to keep track of my appointments and planning projects, and I have all my contacts there -email,skype, etc. Yes, I make phone calls, too. When I go to bed, I like to listen to music, so I connect to my stereo and stream some music from my collection or I download a movie and watch it before falling asleep. I could mention so much more - to me it is the swiss army knife of phones. And yes, it all works - even though I sometime had to tweek it into submission ;-)

3) Why Maemo ?
Because it is open source and it is a full OS. You can even use the knowledge you gain when using it in other similar OSes. Most of the apps are free, and you can get by paying for very little.
It is time-consuming in the beginning to tweek and configure Maemo, but after a while you feel that there seldom is a problem you can't solve (especially thanks to the great forums and contributers). So you get smarter, not just addicted to some company's vision of what you need a phone for, and what they can make you pay for. Donating, when possible is a better way (IMHO)

4) What will be the next "N900" ?
Possibly something like it, only better, but it is highly debated. I think a lot of people, who have been so pleasantly surprised of the N900 are dreading the future. I hope the guys at Nokia will continue believing that an open source phone such as N900 is the way to go, but who knows ? Maybe some other company will take over, where Nokia left, at least I am confident that it is by far the better way.

I hope that the readers of this - my rant/uninhibited opinion about the N900/Maemo will forgive me for being so over-joyous over my phone, but I hope I will never go back to some closed-source, over-hyped, semi-intelligent phone. Thank you for N900 :-)