I updated this morning to SourceTree 1.4 for Windows. When I let the installer re-launch SourceTree, it basically just hung. No matter which of my repos I chose, I just got an endless (I gave it about 5 minutes) spinning icon. It never did show me the status of my repository.
Then, I noticed that Windows in general was very sluggish, so I popped open task manager to find that my cpu (8 core i7) was being 100% utilized by several (8, maybe?) instances of git.exe that had been launched by SourceTree.
I quickly uninstalled SourceTree, and reinstalled version 1.3.3. I will stick with that, until this issue gets sorted out.