1 - anything cached like RSS feeds can be viewed offline, as well as documents you tote with you. gnumeric to open spreadsheets, PDF viewing. there is also a GPS nav app called maemo mapper. you can cache the maps, download a route, and with a seperate GPS device track your movements. you can also watch movies on it.

2 - with the high res screen, there are few pages that you have to scroll left and right with, and it 802.11g enablesd. getting onto hotspots via wifi works well.

3 - yes it will. i actually have 2 8GB SDHC (next gen SD cards) in my n800. many here do, and there is a kernel patch to enable that, should you be so inclined.