However, I've recently started some development with some friends and we are, by necessity, operating in a very 'distributed' manner and we really need the ability to work also in 'disconnected' mode: myself in particular, what with being often working on a train on my way to London...
Having heard about Mercurial and always thought it would be good to give it a go, I decided today to install on my two Ubuntu boxes (the desktop and the home server) and that was as painless as it can possibly get:
sudo apt-get install mercurial
and you're set.
Tortoise is one of the best-written 'Explorer extensions' for Windows and undoubtedly one of the reasons why I stuck along with CVS for as long as I did - there is also a TortoiseHG extension for Linux, and I've (again) installed it with extreme ease.
I will soon try out the Eclipse plugin (that is pretty critical for my workflow) but the first impression is that this really is a very lightweight, yet powerful DSCM (and we now support it on Google Code too).