The default setup for the Mercurial DVCS on Windows with tortoisehg uses plink and Pageant to manage SSH keys when you are using ssh as the transport protocol for mercurial. That’s most likely the right choice for a normal Windows setup, but if you already have openssh installed and configured to talk to various servers, it’s easy to switch mercurial and tortoisehg to use openssh. It’s also very helpful if you’re forgetful like me and forget to start pageant, add new keys…

Admittedly I’m  not the biggest fan of git - I prefer Mercurial - but we’re using it at work and it does a good job as a DVCS. However, we’re mostly a Windows shop and the out of the box performance of Git for Windows is anything but stellar when you are using ssh as the transport for git. That’s not too much bother with most of our repos but we have a couple of fairly big ones and clone performance with those matters.