I recently experienced Visual Studio 2013 loading very slowly at the splash screen. It was noticeable since I'm on a very fast dev box and accustomed to VS 2013 loading very fast (normally under 10 seconds).
So, something defiantly changed.
Problem turns out that I had recently opened a project under Git source control located on a remote share.
The remote share was no longer available, yet, the Team Foundation Git Source Control provider was still probing the network share which took up a significant part of the loading time. I suppose the Git provider was waiting for a network timeout.
Anyway, to resolve the issue simply remove the offending network shares under Git source control located here:
Under the Repositories key, you'll find a stash of GUIDs for each project the Git provider keeps track of. Locate the offending GUID keys that contain the network shares you want to remove and remove the entire GUID entry (along with the contents) -- and all should be well.