I totally agree that software wise we have some major advancement with the N900 over the E90. That said, I would expect so, we are talking 3yrs of tech advancement.
The N900 has a lot of merit, the software foundations really push it a long way up the ladder, even though not refined out of the box.
The simple fact it is open source means it should outlast the E90 and all other phones on the market providing the users are behind it and a demand.

2 years E90 user here. Certain things I miss absolutely are the keyboard along with the D-pad (I used putty an awful lot with the E90), as well as the form factor where you could tilt and hold it in certain positions. Also miss the fact it was bombproof, but I do not miss the exterior screen (far too small), the lack of support for the internal screen from the various S60 apps, and horrendously slow pace of it. It also frustrated me how difficult it was to develop for.

Oh - and I also miss Gravity, but I think Tweego and Witter are coming on leaps and bounds.

For web browsing, Opera really came good with their latest release, but I can't look back with MicroB.

Favourite facilities so far: fcron, mypaint (great for note taking, sketching whatever), knots2, erminig, rdesktop and the fact that most (linux) tools I use daily are just quick install away.

The N900 is breathtaking piece of kit.

I have no problem with this. I just think that the E90 strengths that you listed are such, that if you added them to N900, it would actually become E90 (or something very close to it). A gadget very different from what N900 was intended to be.

Totally agree

i never used an E-series before but looking on my previous and present mobile devices, IMHO, none of them match up with the n900.

though i still like the way the n95 and n86 works for me,