I got the 800 at xmas in the amazon deal. I only use it on the road bike and recently used it in anger as part of a 50mile charity ride up north. I uploaded the official route and it worked a treat apart from trying to send me round roundabouts the wrong way (which is a common problem with garmins according to many). Bearing in mind I didnt know where I was at all, it navigated me perfectly from Wakefield to Manchester over the pennines (including city centres).
Data collection from sensors is spot on and easy to setup. Customisation is good too. Free OSM maps available which helps.
I did think about the 810, but pairing with a mobile isnt something I would use on a regular basis. As said by many above it only uploads to garmin connect which is getting worse as a usable tool (now only uses elapsed time which is a pain). I only use strava now. Tracking would have been neat, but if I had crashed the phone would have probably died anyway so probably not as useful as first thought. The difference in cost between the 800 and 810 is such that I would simply go for the 800.