"One of the many useful features of Webmaster Tools is the ability to adjust settings for your site, such as crawl rate or geographic target. We've been steadily adding settings over time and have now gotten to the point where they merit their own page. That's right, Webmaster Tools now provides a single, dedicated page where you can see and adjust all the settings for your site."

http://googlewebmastercentral.blogspot.com/2008/12/one-place-for-changing-your-sites.html

http://googlewebmastercentral.blogspot.com/2008/12/more-control-of-googlebots-crawl-rate.html

[Linkfix ~ hebbet]

I wonder if they can put a crawl frequency variable into the Sitemaps protocol.

http://www.sitemaps.org/protocol.php

Don't recall if it's new, but I don't remember it before. After changing the settings for a site, Google noted, "Your changes were successfully saved and will remain in effect until Mar 9, 2009."

The only change I made was to the crawl rate. I assume it will drop back to Google setting it after that.