I have: http://windows.github.com/
My current project has around 20k files, around 150MB (and not speaking about how slow it is and I cannot do a thing now) it doesn\'t
You can manually navigate to index.lock which is found inside the hidden .git folder of your repository location. Once you delete index.lock you will be able to commit as per usual.
The easiest way to navigate to the folder will be to click on the folder breadcrumbs inside windows explorer and add \.git and press enter.