Unless you have lots of linux experience, don't get the N810 unless you will be happy with most of the included apps. Many 3rd party apps requires command prompt savvy tweaking.
Simutanious surfing is limited to about 3 windows of basic html and one window if you are using an intensive google app, ex. java, ajax, flash, etc

Most video, including youtube tends to stutter a bit. The N810 is not totally media friendly unless you convert the video files via the Nokia IT Video Converter on a PC first. Meaning, the N810 is not a stand-alone computing solution. You'll be using a PC in conjunction for non-mobile apps and certain websites.

Basically I use mine on two occations.
1. For travelling, using the gps/maps, check email, RSS feeds, etc. lighter then a laptop.
2. Keep it by my bedside for those times I want to check something quick online without having to get up and turn on the PC, or when my wife is into her 3rd hour of Facebook on the PC and I need to check my email.
Other then that I find its easier to use a laptop.