I'm very pleased with this device. Makes a good replacement for both a PDA and a notebook, albeit the "personal information manager" features of a PalmOS PDA are still better than the basic address book in the N800.
But this is no PDA, it's a mobile internet browsing device with Wi-Fi, Bluetooth (you can connect to the Net via bluetooth to your GPRS-enabled mobile phone), and it excells at that job.
Excellent screen size. Three buttons let you zoom text in/out and also go into "full screen" mode.
It comes with a stylus but besides entering URLs and login info the first time(it can save logins for future visits), you can navigate the web and read just by using the 5-way navigating pad on the left side of the device.
It includes two SD slots and can be used as a video and MP3 player.
It runs on Linux OS, with a nice graphical desktop developed by Nokia
You can install dozens of third party applications, most free, including a spreadsheet (Gnumeric), an enhanced media player dubbed "Canola" that makes the device look and act like an iPod, and it's rumoured that Nokia is having Skype port its software to the device as well.
No "extended battery" currently available.
(Battery life is between 2.5 and 4 hours of continuous use when logged in via Wi-Fi (which can be a power hog). If you let power saving kick in, the battery can last for a couple days without recharging).
Do a Google search for "Nokia N800 theinquirer.net" and you will be able to read my full review as published on 'the INQUIRER', including pictures.