If you want to know more about how often Googlebot crawls your site or you want to change the crawl rate, it's time to visit Google Webmaster Tools and to add your site.
Google shows charts with Googlebot's activity from the last 3 months: number of pages crawled per day, number of kilobytes downloaded per day and time spent downloading a page. These charts can tell how often Google crawls (or recrawls) your site.
If you think Googlebot uses too much bandwidth for your site, you can change the crawl rate to "slower". In some cases, you'll also see a "faster" option.
It's interesting to see that Google asks your permission to use the images from your site for Google Image Labeler, an experiment that will improve Google Image Search.
Google Webmaster Tools tends to become the place where you can explore and improve your relationship with Googlebot: you can see its activity, its complaints (errors), you can make it easier for Googlebot to find the pages from your site and adjust some settings to improve crawling performance.