I have all four 770, n800, n810, n900...
The n800 is my media machine for flights/etc -- 32 GB + 16 GB SD cards: books, movies, music.
The n810 is still used mostly bedside for browsing.
The 770 is gathering dust while I try to find the time to create some "project" with it...

I wasn't going to go for the n900 because (from the chatter) it seemed that it would be abandoned like the 770...
I finally went for the n900 back in early Jan. I decided that it would likely be the last really open maemo device, so I figured that I would get one...

It is nice not having to tether to my phone (and only carry one device around). Since I used my NITs with a dumb-phone, the n900 isn't much different than my old setup. Those expecting the n900 to be a smart phone tend to be disappointed -- it is more of a smart device with a phone application.

As mentioned by others, the smaller screen can make browsing/etc a little more hard on the eyes. The camera is pretty good (I needed a new point-n-shoot camera, so the n900 filled that niche for me). The software environment is just starting to pick-up -- most of the apps from the n8x0 line are finding their way on to the n900 and there are a few glimmers of new things coming down the pipe (there is a neat demo of a panoramic photo app that was just released and games like Angry Birds)

Also, as mentioned by others, the system doesn't have quite as many options and they took away stuff like red-pill mode in the app installer because all the new maemo users were doing not-too-smart-stuff and ended up messing up their systems.

I do find the new users a bit off-putting -- they seem loud and obnoxious and seem to not want to search for answers/etc.

Would I still buy the n900? Yes, I really like it, but I am not your average consumer... I like things that present a challenge and learning opportunities. I don't like doing things the easy way.