The issue with the Nseries is that it has no focus.
Non-tech people generally aren't sure what they're for - 'Internet Tablet' is very broad.
Tech people just see Linux Palmtop and immediately think they can do anything with it.

The fact is, as an Internet Tablet, it isn't very good for web browsing - It can't render pages in full-layout as well as an iPhone or iPod Touch, but also can't render it in a stripped-down but purely readable layout as PalmOS units can do.

The video hardware is (According to Antilles and others) too crippled to allow the unit to be a good video player, and this is the experience I've had - It really struggles to smoothly play full-rate FMV that my Zod2 and TH55 can play with ease. I'd say it has about the same performance as my old T665 unit did with Kinoma videos.

While the unit has PIM software, I find it takes too long to pull stuff up - It just doesn't come close to competing with my PDA.

The unit just can't multitask - Load a couple of apps and the thing starts to lag like crazy; Even opening more than one Web browser window causes noticable degredation in performance. If it was using a state-switching system like PalmOS, the 400MHz CPU and 128MB RAM would be incredible, but it is using Plain Old Linux and such a system is just not powerful enough to run a 2.6 kernel and multitask without having more uLinux patches hacked in.
The fact that it has so many tasks running stock doesn't help either - My OS2008 N800 has more daemons running post-boot than my dual-core server!!!!

The resource tightness makes it unstable - I've already crashed the N800 more times in a month than I've crashed my TH55 in years (Tips - Try not to let MicroB+Flash and MediaPlayer load at the same time. Also, delete and recreate your Swap file (If you use one) after EVERY crash; Maemo doesn't sanitize it after crashes and won't notice if it's corrupt; This is exacerbated by the FS being FAT32.)

As it stands, it's a nice toy, but I think it needs a lot of developing before I'll think of it as a useful tool.
Nokia either need to enhance future lines so they're better at being more general purpose, or tighten up the OS so that it's better at what it is supposed to do.