got one, love it!
Be aware that the standard map is of no use whatsoever. I bought an additional topographic map from Garmin at a cost of 125Euro or so (Holland, Belgium Luxembourg). Not sure what the UK version runs at. You could however avoid that by using openMTBmap (google it). Depending on how active the user community in your areas is, the openMTBmap might be equal to, or better than the topographic map. If you decide to splurge on a Garmin map, buy one on a DVD, not an SD Card. The map on the SD card can only be used in your GSP, whereas the DVD-based on can be copied to your pc and your gps. You want the map on your pc to plan routes in advance, that kind of stuff.
Software is freely available and works ok. Mapsource for setting and editing routes and tracks. Training centre to keep track of workouts, training goals, etc. Of course, you can also go online with all your data by plugging it into a garmin connect account.
Consider if you really need to the heart rate monitor and cadence/speed sensor. You could save a few bob by buying only the gps unit.
The touch screen on the Edge works perfect, even with long finger gloves and in the rain. The mounting is probably one of the best so far (although it doesn't look like it). I have yet to loose the device and I like to really hammer it down rutted bumpy downhills. visibility in sunlight is ok, gps unit stays on track, even under dense canopy.
Cons (if you can call them that) are:
Speed measurement can be a bit a slow to catch up with acceleration. Using the speed sensor would counter that.
If it's your first GPS you may have a bit of learning curve ahead of you, but that would go for any device
Operation of programmes like map source and training centre took some getting used to.
Fixed battery, may be an issue on multi-day camping trips in the sticks where you go without power for extended periods of time (solar charging available perhaps?)
Cheers, Giel