The N800 has been a fantastic productivity device for me (no, I wouldn't swap it for an iphone or an ee in a pink fit). That's largely because of third-party tailoring, Addition of GPE, abiword and OpenOffice satisfies my key uses; I would never have bought it as an internet tablet only. That doesn't leave a lot of room for a new machine. However I'd shell out again if it either supported these uses better (esp. OpenOffice), or gave me new ones. The keys for those are:
.video out (vga or dvi - or even better, wireless usb)
.wimax compatibility with Korean WiBro (unfortunately this is a minority requirement )
.min 512MB RAM
Any two of the three would probably sell me; one out of three would be line-ball