I know that it would be a somewhat difficult undertaking to migrate to Launchpad, but it seems like it would have its rewards.
I have noticed that there are a lot of pages here that must require a lot of maintenance that Launchpad provides automatically. Here's a tour:
https://launchpad.net/+tour/indexFor example, the entire ToDo section is basically the "blueprint" section of Launchpad. However, Launchpad's version allows for filtering, better workflow transitions, attatchment to bugs, and easy asignment. Most importantly, it is not a wiki, so comments can be added but the original remains intact from spam. The current ToDo does not allow easy and complete discussion.
In the download section of this site, I noticed that there is an Ubuntu repository hosted. This would be updated automatically on launchpad.
As a user, I would have to do a little looking to find where to submit bug reports.
Having your activity on launchpad might increase the chance it is drafted into an actual Ubuntu repository, which I think would be really cool. All the time I hear people say that Ubuntu needs a good Strategy game and a good First Person Shooter. I believe UFO:AI is one of the best strategy games out there. I know they say that it is because some of the textures are marked with an "unknown" licenses, I'm not sure thats the whole reason they don't have it yet.
The Answers feature could replace several sections of this forum.
I think translations are easier to do on launchpad than Sourceforge.
You can divide and conquer. One of Launchpad's best features is it's teams. Teams can be specialized to do certain tasks, making it easier to manage and figure out what to do. Smaller, specialized teams also seem to encourage new helpers to join.
You can do just about everything by email, like manage bugs. Some people really like to do that, but I never really understood it.
You get points for help. That really seems to drive some people, but really it's just bragging rights for everyone.