Unfortunately, you didn't bring up an EXTREMELY important downside of Open Garden.
I started using it about a month ago when I was looking for exactly what Mischa was describing, where I was sick of fiddling with paring and settings to tether my Nexus 7 to my Galaxy Nexus.
However according to some complaints and responses from Google, the way Open Garden is connecting to other devices (I believe it's done via a VPN) means that a great number of apps think that they don't have a connection when their only connection to the internet is via Open Garden.
There have been statements from Google developers that this will be fixed in an upcoming version of Android, but at the moment apps like Pocket, Feedly, the Play Store, and basically anything other than Chrome or Youtube cannot be used.
This is a really awesome service that I want to make use of but at the moment it's extremely limited.