I use Launchpad for pretty much all of my projects at this point. I have been really happy with it, and I have found that bzr works well for Linux/Windows/Mac. Drizzle, Gearman and others are already there so this just simplifies my daily workflow.
This should help with me being able to take patches a bit more quickly (and for that matter do reviews). Having contributors push their patches to their own trees, allows me to easily pull patches and do reviews. With Drizzle we keep a "staging" tree just so that we can regression test any code before it goes to trunk. Since code in Drizzle goes through several people before I see it, we each get to make revisions on it and look for issues like copyright violations/etc. By tracking code by Launchpad account, we always know who code came from.
For libmemcached I will also be enabling the bug system on Launchpad. While tracking via email has worked, I would like to come up with something a bit more formal.
I've been using Laundpad for over a year now and I am really happy with it. Career wise I have used several proprietary systems, of which Bitkeeper was the best, and several open source ones, of which Subversion was the worst (it was the only system that ever lost code).
All of the distributed revision control systems are pretty good now. I've used all of the major ones and have not really had many issues. The reason I go with bzr really has to do with workflow with Launchpad.
Mercurial is great, and I will continue to use it for a lot of personal projects. It is the only open source distributed revision control system that I find to be easy to host. Its ability to do push/pull from HTTPS is a major asset for me. So for work I do where I need to continue to host the data I will be sticking with it. I completely understand why Google went with it, and I really wish BZR would add this feature.
Looking back over the last few years it is amazing to see how far the revision source control system have gone. Just a few years ago all of the tools were garbage and it was a nightmare to pick one.
Thankfully we are well past that.