1. With Nokia 770 - frequently - whenever I can't find a wifi hotspot (way too often). Extremely useful when we've been on vacations.
2. Motorola V557, about 2 years old now. Pairing was idiot simple.
3. Relatively. Someone posted a script on connecting to the Cingular service here at ITT for OS2005 and I've used it since (currently on latest OS2006). I didn't get the built-in Cingular/att client script to work, since I have one that does work, it's what I use.
4. Cingular/att
5. $20/mo (probably same plan as Thoughtfix's) for unlimited data (MediaNet service). I am not sure if it's really intended for use with tethered devices vs the phone itself (handy for Google's mobile services) but it's worked for me.
6. Wifi is much faster. No idea unless/until I upgrade to a newer phone if we have faster service in this area.