Some people are being a little hyperbolic here; You can read the N800 screen in direct sunlight, with large fonts, white on black, and backlight all the way up -- but it's very hard. It's quite readable for web browsing etc. most of the time outside, as long as the backlight is all the way up. Mapping, at least with hybrid maps, is not very readable outside, short of seriously shading eyes and N800 with one hand.

It is bad in daylight, and I'm sure the N810, being transflective, is loads better. But it's not all that unreadable outside.