The OS project I work on (disclaimer: I work for the company that “backs” the project) just went through the process of finding a replacement to the project's traditional mailing list for a lot of the reasons that people have raised on this thread.
We ended up settling with GetSatisfaction which, although not perfect, solves many of our problems and importantly is focussed around getting answers to questions and solutions to problems. I think this list has similar kind of content.
Our instance is at http://forums.gradle.org/.
Just throwing this out there in case anyone is interested in taking this further. If anyone wants to ask questions about it I'll happily answer.
Cheers.
LD.