I don't currently have a 770 (I've only had the 810 for about 10 days now), but given the low cost of used ones I might pick one up shortly if it seems enough others are interested in a deblet port. For daily use I'd definitely stick to the n810 (mainly because of the keyboard, but gps is quite handy as well), but functional debian on a 'cheap' 770 would be great for many tasks.

Some quick brainstorming:
1. Portable snort node
2. portable kismet node
3. remote for home automation (x10, etc)
4. handy x display for headless workstations/servers
5. travel router (does the wifi chipset support 'master' mode?)

Given that these are such small devices and linux capable, you could use them for just about anything. The 770 has the advantage that you can buy used ones for ~$60-$100 means that they're close to the price of a linksys wrt54gl or netgear wgr614l, and much smaller/more capable (plus you can view the battery as a builtin UPS). I'd consider using a ~$75 770 in a lot of applications that wouldn't be options for a ~$350 n810.