I'm starting to move most of my projects off launchpad onto bitbucket.
launchpad just hasn't gone in the direction that is useful for me, or my projects.
It still has some nice features, such as packaging farms (PPAs) and of course bzr integration. However, github and bitbucket have just been moving more towards making it easy for developers compared to launchpad which is more geared towards for distributors who work with an upstream. Last year I hoped launchpad would improve after it went open source, and it has improved. Just not really in the direction useful for my projects.
Many people these days are able to use hg, or git... but still very many people have never even heard of bzr. I feel bzr+launchpad was holding one project back a little from gaining collaborators because of this. By that logic, I should be using svn for it... but I don't want to do that :)
The documentation to convert repositories to mecurial is on the hg wiki. The conversion seems to mostly have worked ok for me on my python newsletter project. Except it did not put the correct email address attached to each of the commits. Oh well.