This has come up a few times in:
The solutions there were to search using Google. Like MMyers says in the top linked post, I also use comments to find "where I was" when I can only vaguely remember what I said, and I didn't leave an answer myself. So, I might remember I said something about "database logic" and the discussion had PHP in it. But using Google and SO search, I couldn't find the comment (I only found it by clicking thru my comments chronologically).
(The comment I was looking for is here.)
Having a (search) filtration box that filters fetched comments by keyword would be useful.
A search box is added unobtrusively to the top there.
Notice how small my font is when searching comments. Because the "next" button is out of view, I'm trying to zoom out enough so I can scan comments for what I'm looking for without having to scroll too much.