This seems logical, however what about the person who updates rarely (once or twice a month) but get a lot of notice when they do. Search engines wouldn't want to miss the opportunity to get that traffic. I wonder if there is some sort of reverse process you could opt into - ie never crawl me until I ask to be crawled. Disclaimer: I know little about this sort of thing.

Sitemaps (http://www.sitemaps.org/) help a bit in that regard, as crawlers can check the sitemap and only crawl updated content.

PUsH: http://en.wikipedia.org/wiki/PubSubHubbub

Google is the only crawler I see using the protocol on my site. It does make Google updates occur within minutes, so that alone is reason to implement push.