...and in this case, since I'm the developer, what does that say about me? I just discovered that when I wrote the code to produce the comments feed for my blog, I screwed up. Rather than giving the past x days of comments, my comments RSS feed was giving all the comments for the past x days of entries. So if you commented on an entry that was more than x days (I think it's something like 10 or 14) old, then it wouldn't ever show up in the feed. I noticed this by accident when cross-linking to my old IsNot post, and now I think I've got it fixed.
So if you've submitted some comments and I totally ignored you, it might be because I was relying on a broken comments feed. Then again, it could be because I'm a lazy bastard... You'll just have to guess!
(I will be going back through all my comments to find ones that I might have missed...)