For most of us, yes, it's a good buy. For me, it's definitely a good buy; If I have the money, I would buy another one.
But that's me or for most of us here.
It depends what you want, what you're looking for, etc.
The N900 is a mobile computer (Internet Tablet) with added Phone Functionality.
The OS is beyond or higher class above smartphone OS level; after all, it's an Internet Tablet basically.
You can think of it as a notebook/laptop, with touchscreen at the size of a handphone, then slapped on with phone funtion; The major difference is, it's running Linux based OS instead of Microsoft Windows, and the spec is only 600Mhz with 256MB ram (+768 Virtual Memory).
If you're emphasizing on phone functionality, or phone functionality is important to you (e.g. 3G Video Calls, MMS, etc), then you might want to re-consider. This N900 phone functionality, is very basic (although now you can extend some of it's features via 3rd party app/plugins).
The thing you'll appreciate is the integrated Instant Messaging accounts into the phone book, and also the CONVERSATIONS where all your SMS and IM messages is kept. You don't need to run anymore 3rd party social networking applications anymore. When you go online on the N900, it will auto login to these IM you set.
You'll appreciate the multi-tasking as well, because it offers true multi-tasking and it's very nice.
Web browsing is also splendid on this device, you can browse Desktop version web page; You might even don't want to use your laptop anymore, you can browse on the N900 almost anywhere conveniently.
The cons of N900:
1. Not much games like those in iPhones; Altough now there is WebOS games, but with lack of multi-touch, those games that utilize/requires multitouch will be hard to play or unplayable.
2. Need patience and willingness to learn and improve yourself with skills/knowledge; It is a complicated device afterall, but it'll help you become a more knowledgable and skillful user in technicals areas.
Basically, there's many pros of the N900, but depends on what you want and what's important to you. If you don't care about all those, the pros of N900 will become meaningless to you.
owh and you forgot to mention we can boot into several different OSes..
1. Maemo - default OS
2. NITDroid @ Android 2.1 -
3. Ubuntu -
4. SHR @ Stable Hybrid Release -
5. Meego -
6. Easy Debian -
7. PalmOS Garnet VM -
8. LXDE (via Maemo/Easy Debian) -
but this are only for people who knows what they're doing and understand the risks of having to reflash/reformat the phone..