As an E90 owner...
I have the E90.
I purchased the phone, here in the States, as an unlocked model. (Kinda pricey).
The reason for the purchase was that it had GPS and that it also had a large QWERTY keyboard. Something that is a bit of a necessity for someone who does more e-mail/texting than phone calls.
With respect to calls, I can use either the head phones or a blue tooth head set while my phone is in my computer bag's outer pocket.
I like the idea of two screens. The truth is that the outer screen is ok for a quick look up of a contact, a quick mapview, or a quick look at your calendar. But to read any e-mails, look at a pdf or web page, forget about it. The inner screen is a must have.
I'd like to comment about the built in camera on the inside. In the states, its useless. There needs to be an app that allows you to do vid conferencing while connected to a wi-fi. (Ok, I'll wager there is one, but I haven't seen it.) Or a decent IM package that would let you do vid conferencing. I'd also like to see a better wi-fi arrangement because the phone tends to drop the wi-fi connection or "time out" when you're reading a web page and not making wi-fi requests.
Overall, it does what I need it for, but its still far from perfection.
It is big. Friends call it a brick.
There phone is on 24/7 and I sometimes have to reboot the phone on occasion to get it to work.
If Nokia was working on something, I'd rather see the N810 successor that has wi-max/wi-fi capabilities, a cell phone (not wi-fi only telecommunications), and some expandability. (Heck wouldn't it be nice to be able to plug in modules like telephone service, wifi or wimax depending on where in the world you live? A USB port, and some external memory.
IMHO, while the 810 is bigger than a phone, its still usable in most situations where one can carry it in a purse (ladies), a backpack/briefcase/laptop bag, and use a blue tooth component to access it. Its definitely not for the "petite" phone first crowd, but for the businessman who doesn't want to carry a laptop and its components around everywhere, plus a cell/blackberry.
Thumbs up because the E90 and the N810 show convergence of technologies that isn't aimed at your traditional tiny hand consumer.