A question I was working on which sparked this meta-question is mostly about things which must be avoided in a specific file of programming, but for which it is not readily obviousl that it's necessary to avoid them.
These are normally termed "gotchas" or "pitfalls", two words which are used in plenty of questions on StackOverflow. Here's a couple I spotted which have lots of votes:
-  What are the biggest gotchas in Silverlight?
-  pitfalls/gotchas of click-once/smart-client deployment in .NET
Yet neither term exists as a tag on StackOverflow.
Could it be that either or both of them have existed over the years but have been nuked?
Could it be that they would be viewed as "meta tags"? For, as we all know, "meta tags are bad".
OK it is said that each tag should be capable of being the only tag on the question as a test whether it's a good tag. I think that could be too strong though. While it wouldn't be much point to watch such a tag on its own, it would certainly make a lot of sense to watch it in combination with your other tags of interest, which is what the "interesting" questions tab on the site's front page is for.