My personal favorites are effective game-breakers for branch-of-users-X, possibly more, which should take minimal effort to fix (unless the architecture is horribly screwed up), that get 100+ submissions as duplicates, reduced test cases, discussions, pasted diffs hoping someone, please God anyone with commit privileges will look... and they get ignored for years.
Looks like in cases like that the bug tracker is making the underlying problems more visible. In that case, removing the bug tracker is not the way forward.
