I've had my n900 for a few days now and so far I'm very impressed. Having a full linux environment in the palm of your hand is simply amazing. Coming from an iPhone 3gs I was interested in how the interface would compare and I have to say the 3gs beats it pretty easily. I've read from some how much more accurate resistive screens are when compared to capacative, but I never had any accuracy issues on the iPhone and touchscreen on the n900 definitely isn't as smooth. That said I'm still impressed by the touchscreen it is very responsive and I haven't needed the stylus to navigate at all, scrolling is the biggest issue with it and even that isn't too bad.
The lack of multitouch hurts the browser experience a bit, the swirl gesture is easy, but not nearly as quick as pinching to zoom on the iPhone. I'm liking the browser though, the iphone's browser is great, but this feels even better. The resolution increase definitely helps it feel like a desktop class browser, not to mention the ability to install various extensions to it.
The lack of an app store hurts. The app store for the n900 isn't even available yet, but if you go to maemo.org they show you how to get an early look at what is going to be available and it's pretty pathetic. That said, there is a ton of linux software that is available and more is coming every day. Duke3d runs great on it and dos box performance is decent.
I'm really liking it so far, but it's definitely got some issues. There is no Exchange 2003 support, only 2007 which means I can't currently use it for work. Luckily that has already been patched and is coming in the next firmware update. The battery life seems pretty bad even under light use, hopefully it can be improved with firmware updates. Flash in the browser is overrated, performance is pretty poor on most sites. It works fine for youtube, but most other sites are pretty choppy, especially for live video. I'd rather just have a youtube app rather than navigate to it in the browser and I have downloaded the one I found available. I was a bit worried about switching to TMobile, but so far at least here in Topeka their coverage seems as good as AT&T and they've got HSDPA access rolled out here so the internet is incredibly fast.
Here are some images I took while I was playing around with it: