Nicest of the Damned: Nice spider…
The question becomes, “should everyone on the web be sending out spiders?”
Or, another way to look at it: maybe a few people run spiders and the rest of us subscribe to them? It’s another aggregator, but based on content/context, rather than novelty. You get to unravel the web and weave your own.
I’m not opposed to spiders — they’re just fast automagic browsers — but I’d be concerned if there was a lot of repetitive crawling.
Another aspect of this would having it learn or suggest keywords based on a thesaurus or even note new words in proximity with your keywords: using the EvilBot, if bin Laden drops off the index of evil, perhaps he’s replaced by someone else and their name is suggested to you as a possible additional keyword.