"The crawler could not communicate with the server. Check that the server is available and that the firewall access is configured correctly.."
This error sometimes shows up in the Crawl Log in the SSP.
The issue in my case was a custom database that the crawler account did not have access to. Of course an easy way to figure this out is to login to the website as the crawler account -- to see what it sees... It worked. A quick adjustment of SQL permissions and voila, we're crawling again.