Mailing lists are essential forums for a huge number of open source projects. We're not the first to use them and we aren't going to be the last. I agree that it's perhaps not "webby" enough but that's what we've been using since the beginning and it's what we're using right now.
How about a plain old online forum? That would certainly be "webby" enough and not require much in the way of extra resources if you're already hosting mailing list archives.
In fact I'd argue that it would probably save bandwidth as then you don't have to mail everyone every time someone posts something which not everyone wants to read.
