Hi RC
Here is what I like besides all the standard basics
1. User friendly - large color screen, joystick
2. Navigation - ability to purchase and upload 24,000:1 maps on a micro-SD card, great if you road bike. It works like a car GPS then, and you can actually use it as such. There are free maps one can download as well, but some technology knowledge is required. Unit comes with base maps, which are adequate for MTBing.
3. Garmin Connect and MotionBased - free web services from Garmin that allows customers to store, view and share activities/locations recorded by you and other Garmin users. Motion Based will eventually be folded into the Garmin Connect (GC is limited to only a few Garmin models incl 705 for now). Here is an example of Garmin Connect and Motion Based.
http://connect.garmin.com/activity/1687413
http://trail.motionbased.com/trail/activity/7259656
Also included is the Garmin Training Center, a seemingly 1980's locally installed application, which does do the job.
5. Can integrate with 3rd party power meters and slew of other accessories.
6. Good battery life
7. Looks just like a regular USB drive on your computer, easy to drag and drop your routes and such.
What I don't like:
1. Mounts - will come off if jarred by say something like an endo or tagging any fixed object. Same as the 305 I used to have ...
2. Lack of included detailed base maps, for a fairly expensive unit.
So you can imagine with harnessing both the possible monitoring hardware like HR, cadence, power; AND the social app side like the network of users' maps and routes, this becomes the only piece of hardware you will need.