I cant talk about N810, but i cant talka bout WebDT and Nokia 770.
I first bought Nokia and was amazed with its funcionallity. But the screen was too small for me. I bout WebDT and immediately forgot about Nokia; WebDT is the best thing i ever saw as an Orbiter (i have also Fire Chiief, Nokia N95 using JAVAMO, and Nokia N70). I have 3 Webdts, 2 are mounted on the wall and use as "central" remotes for the room they are in, and one is "mobile orbiter". I have to charge that one every day, but its worth the hassle. Just like i charge my cellphone every day:D.
IF You have the money for Webdt, go for it, You wont regret it, trust me.