Two friends and I started Chaos2D yesterday. We ended up deciding to use QtCreator as the IDE and Launchpad (Bazaar) to manage the project. We downloaded Bazaar Explorer, naturally, and the fun began. This post is a guide for my past self; I'm sending it back next time the DeLorean passes by. Note that my experiences are from Ubuntu 11.10, but of course you have that by now.
Firstly, in QtCreator select Tools > Options > Version Control > Bazaar. Enter /usr/bin/bzr in the Command field, and also fill in your Launchpad username and password (I'm not certain those are required). I guess QtCreator doesn't provide for getting the source, but once you have a Bazaar repository it can take it from there.
While typing this, I couldn't remember a detail and had to get some help (important!) from Google. I think I also had to make an OpenPGP key to get Launchpad to acquiesce to my request.
Then Bazaar complained about not being able to authenticate Launchpad; I couldn't find anything on Google about that, so I just said yes and it added Launchpad as a trusted site. At this point I decided to sign the Ubuntu Code of Conduct since I had the OpenPGP key anyway.
Finally, I didn't like retyping my SSH password every time. This is apparently the proper, secure solution. I didn't know about it at the time, so I did this and changed my Launchpad password to something I don't use promiscuously.
Oh, I almost forgot. Bazaar Explorer seems to ignore all ignore rules, so I recommend directly using the less-bold bzr command. I might have said that anyway, after this bizarre experience.