Yeah, so what I'm seeing is that if you have multiple projects in a solution, use packages from multiple sources in the different projects, and not all packages exist in all sources, then VS freezes if you don't have that file in there. I'm going to go out on a limb and assume you know more about this than me ;) but I've been able to repro this on two machines and a VM instance.

The source machine had used a local network repo with a package that didn't exist on the default NuGet feed. I noticed at one point that one of the projects had been checked in with its packages directory, the other three projects did not.  The three machines where I observed the problem were clean VS 2012 installs and didn't know about the network feed.  Two hard crashed in about ~5 mins as the solution loaded (the UI never became responsive after ), the third I never let time out.

What I missed however is that it's supposed to be respositories.config, not packages.config. Apologies there. I commented on a thread back in February here: http://nuget.codeplex.com/workitem/1241 There have been other similar issues as well that I've seen, so I'm pretty sure I'm not alone here. 

I can remove this notice if you think this is an edge case, or correct it to repositories.config.  Thoughts?