Om Malik just posted a quick review of the Nokia 770:

The switching between the applications - email, audio player and browser was sluggish, but the Nokia representatives say that it should be fixed by the time device ships later this fall. The four way keypad navigator works nicely and helps you toggle tasks nicely. One of my concerns was that it would be too big to be used casually, but that is not the case. The ultra-bright screen makes up for the size, while it is light enough to be thrown into your messenger bag without inducing any permanent damage to your spinal cord. Now I cannot wait to get one for a full blown review.

Previously, he wrote about the Nokia 770 saying:

…the linux under pinnings make it more extensible. I think there will be more hacks for this device very quickly. With WiFi becoming common place, at least on school and college campuses, this one has a potential with the next generation.