I get way more spam comments than genuine ones. I often have spells when I'm too busy to tend to this blog, so I used to think that it would be better to let anyone comment, and take the chance of spam, rather than keep people waiting till I managed to find time to approve comments.
But I've really had it now. I don't get many real comments anyway, these days, yet increasingly I get so much spam (the spammers seem to be better able to solve the CAPTCHA than me!) that I seem to be spending more time deleting spam comments than answering real ones or writing new posts.
So I've turned on comment moderation. And I'm leaving it on until there's an easy way to bulk delete unmoderated comments (or Blogger introduce better anti-comment spam tools).
So if your comment doesn't appear on a post immediately, you'll know why. Sorry about that, but that's how it goes.