Personally I don't think it's a good idea to use Stack Overflow like this. By all means use it as a "secondary" support system, but I think it's a good idea for an Open Source project to have its own set of mailing lists/groups and bug tracking system. Most hosting sites (SourceForge, Codeplex, Google Code etc) support this out of the box.
Aside from anything else, SO isn't really built for discussion which you should expect to be part of what the mailing lists etc give for an open source project.
Additionally, users would have to "understand" Stack Overflow itself to grok why all these extraneous questions were appearing when they only want to know information about your project. Yes, you could link to your particular tag - but you'd see an awful lot of other stuff linked etc. You'd at least need to explain this in the documentation.
As an example, Marc Gravell and I have certainly answered plenty of Protocol Buffer questions on SO - but I think it's important that we also have our own "proper" sites with bug tracking etc. You may wish to suggest a tag for people to use if they do want to ask a question on SO (particularly if it relates to how to use your project with something else) but I'd steer away from making it the primary support system.
