[...] The N810 & N900 are essentially based on two very different concepts. The older [circa 2007] N810 is based on the concept that it is a pocket PC which runs on a miniature Linux distro. The "newer" N900 [circa 2009] is based on the idea that it is a cellphone, and it works as a cellphone proper... an outdated one. I already have a cellphone that can do more than the N900. It seems redundant to me to have two cellphone. The N810 supplements my cellphone because it works as a mini computer. The screen of the N810 is also much larger [~4.5in], compared to the ~3.5 of the N900. The N900 is also made from creeky cheap plastic, whereas the N810 is made from metal... I think titanium.
The interesting aspect is, to people who know about the technology, they are very similar devices, with the N900 being potentially more interesting (because the hardware, which is very, very, very similar to that of the classic 600Mhz Pandoras, is faster than that of the N810). This is because BOTH of them are running on a version of Maemo, with, basically, the one on the N900 being developed further. So, the basic system software is very similar, but the graphical user interfaces of these two devices are very different, due to the fact that the more finger-friendly interface of the N900 was regarded as superior for this smartphone-like device.
In other words, if you can do something on the operating system of one of these devices, chances are that the same thing can also be done on the other device. If you still have them, you can install a regular desktop-like system on them, like on the Pandora. I don't own any of these Nokia devices myself, but this should lead you into the right direction: Easy Debian
As far as the Neo900 is concerned, what's special about the Neo900 over the N900 is not that it runs forms of Linux, because both of these devices were built specifically to do that (as were the N900's ancestors).
So, unless I misunderstood you somewhere, the reason why I find your first experiences with the N810 and N900 so interesting is that the way the graphical user interfaces of these devices work influenced how you perceived their capabilities. I have been observing a couple of similar patterns in other situations over the past few years, and think that they may be helpful in improving the user experience and usability of open handhelds. Mabe you already know that the Pandora comes with "MiniMenu", an alternative user interface (here is a video about it: Pandora - One vid per day 9: MiniMenu overview
). MiniMenu is very different from the usual desktop that runs on the Pandora ("desktop" in this case means the user interface with the taskbar, the windows and everything else that would normally be found on a big computer). It'c conceptually closer to a smartphone-type user interface than a typical desktop-type user interface.
If something like MiniMenu would have been the default user interface of the Pandora, maybe you would never have found it very interesting.