I've used the HTC WinMo 6.1 and 6.5 devices (TouchHD, Diamond2 etc) as well as Nokia N95, 5800 etc Symbian phones as well as using my friend's iPhone 3GS. To me, N900 is the best out of them all.

It's very user friendly. My friends figured it out pretty quickly. My sister was using the N900's camera and sending the pics to herself via bluetooth all by herself on the very first go. (She's VERY far from being an IT girl) Like any new OS, it has a learning curve but it's very easy to get used to. Nothing special compare to any other phone. Even the iphone has a learning curve not too different. (Well, it's more confusing in certain aspects such as you can't just transfer mp3's etc over bluetooth from other phones/pc)

As a phone, it does the job nicely. Everything works as it should. Nothing too surprising really. As a web browser, there's really no competition to the N900 currently. Also, the video playback capability is second to none. Plays nearly everything you throw at. (Except for HD resolution vids)

GPS/Maps isn't as strong yet. Just weak software. Hardware is fine. Expect Sygic navigation software to appear soon and you can still always use google maps. (through browser just like any desktop pc)

Music player also isn't a strong point. Audio quality is fine, but there is no equalizer on it yet.

There are tons of apps / mods in the current maemo.org repositories to keep you busy for weeks however. So hopefully by the time you find out about most of the stuff here, there should be a new firmware update from nokia, ovi store will open and more apps/3rd party apps appear.

All up, I expect it to be much more full featured (by firmware updates / more apps) within 6 months.