qgil's last post sounds good to me, except for:
In my experience with other projects (e.g. MythTV) people don't like their bugs marked as invalid - it gives off a rather 'rude' feeling. (Note that this is probably largely just a problem with the terminology used in Bugzilla). Instead, if someone could actually turn the bug report into a brainstorm idea for the user, rather than make the user do it themselves, that might be better.