I wonder if Jakob Nielsen would have popped a vein and died on the spot had he tried another mobile platform or tablet. Really - 7 users? A handful of apps? And how does the developers' lack of HID adhering make the iPad itself "unusable"? Really...
Also, a lot of the problems he has with the iPad do not show up on the N900. He would probably like that.
IMHO, that "buttonless back button" is perhaps the best thing about the N900's UI design.
It sounds like you simply tap anywhere but the dialog and it's "canceled"?
Yes. When a modal dialog is active, Maemo also blurs and darkens the background so it's obvious that it's inactive.