Its web browsing is good, though sometimes it gets a lil overloaded and crashes on sites with poor coding or excessive images/videos (ie most myspace pages or any other sort of site). The touch screen keyboard is adequate, but most users opt to buy a BT (bluetooth) Keyboard for it, they sell some that fold up into a small case smaller then the n800 itself.
(google images for bluetooth keyboard will show you more)
The device's OPS is a linux OS, called maemo. Very lite weight. It has flash 9 and can handle videos like on youtube, though you have to wait for the entire video to load, cause it cant stream very well. Despite being advertised to use voip and skype programs including a built in web cam and microphone, because it is on a 802.11 b/g wireless it often gets laggy during voice/video chat and ultimately frustrating. As a PIM (personal information manager) it does fantastically, though there are no PIM programs installed by default, a quick trip into the irc channel on freenode (#maemo) you can get step by step help from a large community helping you to tweak it out to install the best programs, with all the ease of linux in the app man.
I have successfully set up all the computers on my home network with VNC server software and a VNC viewer on my n800, allowing me to manage all my computers from anywhere, and with a simple ssh into my server, I can access any of my files and stream them online quite easily, I stream music daily with very little lag.
Overall rating of the Nokia n800 is as follow
Video Display: 7/10 (Nice looking display, but little graphics memory allowing for proper display of most videos)
Internet Capability: 9/10 (Display most websites flawlessly, though there are still some compatibility issues that need resolving on some sites)
Sound: 6/10 (Sound is crackly through speakers)
Usability 10/10 (Very useful as a PIM, and an IT aid, recommended for anyone in the IT field.)
Any oppinions are welcomed...