What are they good for? Is <del> the "semantic" counterpart to <strike>? What do the others map to?

Yes. INS is to U as DEL is to STRIKE. They are useful when you update a node.

Q is a tag to produce quotation-marks in a "semantic" fashion, but it's poorly supported by the browsers.

See this HTML specification for more details. Here's the section about Q.

In reply to Re^2: INS, DEL, Q tags now allowed in posts by ambrus
in thread INS, DEL, Q tags now allowed in posts by ambrus

Title:
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