Author: D.Daster (11 Oct 10 10:33pm)
I do tend to second this claim. I believe that occasionally the httpBL occasionally stops returning for clearly malicious IPs.
However, i might also point out that even if you receive spam, and then look it up on the website, you might not realise that the entry is quite new. What i mean is that at the time the spam was received, the bot may not have been identified, but when you noticed the spam, and looked it up, it was known. A span of a couple hours can mean the difference between an unknown IP, and an identified spammer.