I use 1, 4, and 6 all the time. Works great for me. (On GPS: I only recently got an N810, but its GPS seems fine to me; I know they catch lots of flak for GPS problems, but mine does fine using AGPS; locks outdoors, but among buildings, within 30 seconds, and keeps a lock in my jacket pocket while cycling. Maybe some units are worse than others, and I got a good one, or maybe the problems are over-hyped.)

For 3, all my NT machines run Cygwin and OpenSSH, so I generally use sftp; I've heard CIFS is fine, but I can't confirm that. Bluetooth file transfers also work fine.

I've played with 2 a bit, more for curiosity than interest, and it does ok without re-encoding most video content, using mplayer with appropriate lavdopts. Playing arbitrary video is not near as bad as it's made out to be, and it should be pretty good indeed if you reencode everything.

Flash, OTOH, may be an issue; while it usually works fine, sometimes it's slow, and it's always a battery hog. It's the only possible sticking point I see, but if you run a 400MHz PIII, I don't think a 400MHz ARM11 will be a disappointment.