Google just announced today that within their Webmaster Tools utility you can now receive automatic alerts when the Googlebot experiences a jump in Crawl Errors. You can read the whole post on the Google Webmaster Central blog.
There are many reasons that a search engine bot might get a crawl error on a site. It’s actually pretty common. The significance of this update from Google is that they will alert you to an unexpected increase in crawl errors. Maybe something went wrong with your database. Maybe there’s a typo in a bunch of new pages you posted. Maybe a site you link to heavily is down or changed their URLs. No matter the reason, this is good info for a site owner to know.
Additional tip: Google Webmaster Tools is something you should be using already!