[posting this so I can find it again]
The other day VS2010 was completely stuck when “Preparing to deploy assemblies to the device”. After searching for a while, I found this post on the Netduino forums: Can no longer deploy. In my case, the initial ping while in “pre-boot” mode (step 2) didn’t return. But I just went ahead and hit the “Erase” button anyways. Worked like a charm.