For me ActiveSync is a very useful feature for using my PC's internet connection on a WM device to test things like connecting to my webservice running in the cloud or local LAN. Its called reverse tethering in Android world. I also used it in the past for syncing data through Rhoconnect, but that was for local LAN, not cloud, but I believe its possible for cloud too.

Basically, I use ActiveSync just for getting network access, but I use AsyncHTTP or network API or Rhoconnect to actually sync. Others may have used ActiveSync as a 'syncing engine', but for me, I dont even use it to sync my phone address book!

BTW, Ive also used ActiveSync for an 'always connected scenario' Rho app where I connect directly to SQL Server thru a ROR local webservice. Here, my app just provides the UI, but data is not stored in the device but in the enterprise backend.