I have the N900 now for one week. In itself the device is great but, and as you can read on the other forums, there are some issues.
Good, compared to E90:
Large screen, bright
Smaller phone
Fast
Multiple applications
Fast internet
Memory
Ease for calling (most important)
Internet, SMS, mail, etc.

Not good, compared to E90
Reception, old fasion GSM sounds when calling
Set back in software wrt
1. office apps (only view, not edit),
2. OVI navigator, from V3 to V1,
3. Mail for Exchange does not work with the server from work. Even though this is due to the settings at the server at work, the E90 did work!
4. Bluetooth does not always work, not sure why
5. Linux, I am just a user and all the programming stuf and root access is certainly not something I will ever due although I know that it could be very usefull.

Al in al I am happy with the phone and gives the required advantage and hope that the next update solve the mail for exchange issue together with a light weight office application that can edit MS office 2007 docs would be great!