Bought an Edge 800 3 weeks ago or so. Absolutely love it! Still haven't got my head around all the functionality of it (steep learning curve), but impressions so far:
Great to see the heart rate monitor. All data fields are customisable so you can set your own heart rate zones and have the gadget give you alarms when you're not in whatever zone you want to be. If you're into workouts then this can help to set and reach targets. Rode 60km the other day, nearly all in D3 (130-150bpm) specifically to help build up endurance. During the next ride more focus on d4&5 to help build power. Great fun! And afterwards you can see where (on the map or in google earth) you peaked (or slumped) and what you pace, speed, altitude, etc was when you did so.
Navigation and rides:
Brilliant! I recently moved to a different region in the country, not knowing my around that much, and usually riding my bikes when others are working, the GPS is great 'cause it allows you you to download routes from others (plenty about online, check www.gpsies.com
for example) and ride them with step by step navigation assistance. Lock-on to satellites works very well with the Edge800 also under tree cover, although I am curious to see how that works in summer, when the canopy is more dense. Better than with previous models according to Garmin, but then they would say that of course.
For me this is the best cycling related buy since a looong time
Idworx Mountain Rohler (2007)
Dekerf ST (1999)
Roberts Dogsbolx (1994)