This comes up in the crawl logs:
Access is denied. Verify that either the Default Content Access Account has access to this repository, or add a crawl rule to crawl this repository. If the repository being crawled is a SharePoint repository, verify that the account you are using has "Full Read" permissions on the SharePoint Web Application being crawled.
Now, this happens for a bunch of sites that only have one thing in common, they're static HTML.
This isn't a loopback problem, this happens no matter what site I point it at. It shouldn't be a content-access account problem because, hey, these are public-facing sites. What's going on?