I see, I think private tags are worth considering but right now our list is so long that anything I say is conjecture if added to the end of it. One question I have is why ignoring isn't a better solution than that. For example, what purpose does the heads up serve for you?
Another thought is whether letting users vote on tags. For example, if someone things 'tag1' is useful and adds it, but someone else doesn't they could negative tag it (e.g. "-tag1") and it would count as a vote against that tag, requiring another user to use the same tag to put it back.
One of the keys to making the tags relevant to the most people is to just rely on more users to make the tag. If they are being more... creative in their use of it it is less likely that it will match another user's tags.
Hmm, well in any case there's a lot to think about but not a lot of our time to spend on it right now. We have other a2k changes in the works and this kind of thing is going to have to wait quite a while.