I suggested introducing the bugs tag.
Tags are useful for finding things quickly. From MathGroup experience I know that it is useful to be aware of certain bugs, and I have spent time searching MathGroup for descriptions of old bugs that I didn't remember completely. For example, in version 6,
Tally is buggy when using custom comparison functions. In version 8,
IsomorphicGraphQ is buggy (some of the bugs have been fixed in 8.0.4). If I use
Tally in an older version, I need to know which version fixed the bug to make sure I won't have trouble. For this, I'll search for it on MathGroup. If I use
IsomorphicGraphQ, I will want to know what triggered the bug exactly, so I can try to avoid it. Again, I would search on MathGroup. Unfortunately finding old MathGroup posts is usually a pain.
I think this makes it clear why I wanted to make it easy to find bugs here on Mathematica.SE. Tagging posts which have been resolved as bugs is valuable.
The problem with a bugs tag is that people will add it to anything they think is a bug. When people complain about bugs, often (I'd say, most of the time), it turns out not to be a bug (at least a bug that's useful to know about). Often they're misunderstandings, the OP just wants something to work differently, missing features, and so on.
So I suggested that the bugs tag never be used on new questions. We add the bugs tag only when it was confirmed that there is really a bug.
What does it mean that the problem "was confirmed to be a bug"? I don't think it's necessary to have a big discussion about this. I want to have the bugs tag for very practical purposes. So let's just use common sense. If the community seems to agree that it's a bug, tag it as a bug. If people say they can't reproduce it, or people explain in comments why this behaviour can be desired, or it's just a missing feature or a very very minor glitch, then don't tag it.
the tag's purpose is to make it easier to find bugs, so we can avoid them or work around them more easily (I have searched for information about bugs I vaguely remembered many times)
tag it if the community agrees that it's indeed a bug and it might be useful to know about it