1. Web surfing rules if you browse light sites. Some sites will 'freeze' the tablet. I tend to use the mobile versions where applicable. For example, gmail html version is very fast compared to full gmail and gives up little functionality.
2. Vagalume rules. I haven't found a UPnP player that is perfect but MediaStreamer is the best I've found. I don't play from local storage. Battery life is not as good as a dedicated player.
3. FBReader rules. End of story, get it and be happy. It will read anything and I can't think of anything I'd add to it.
4. Office - sorry I don't have any input here.

Frank