Recently I had to use Mercurial to checkout the NetBeans sources. Well, since the instructions were for the whole NetBeans repository, I followed them and I have a local checkout of it. Now NetBeans is big, so, you could think it would take me some hours to get the whole thing, even more, if you consider that it clones the whole repository with the full history. No, it was surprisingly fast and its command line interface is very easy to use.
Alas, I have currently no project where this or other distributed SCMs are used, but, when I get a break from ArgoUML and start experimenting with open source projects from common-lisp.net I'll have a good change that they'll be darcs based.