Methods to determine if someone is hotlinking?

Inspired by some previous (and current) threads re: whether or not hotlinking is Evil or merely evil, I’m wondering what ways can hotlinking be detected without actually seeing the links on the site?

The only thing I can think of it google’s link:www.XXX.XXX feature. I presume that web site control panels may have something, but how about blogs or web sites like geocities that are hosted elsewhere with minimal control by the poster?

You presume correctly. Webhosts generally provide log files and, often, nice interfaces for the site operators to view them with all the information neatly catalogued and sorted. And there are also third party tools that can be used to view these log files, as well. In the case of freebie sites like Geocities and Angelfire, the hosts generally don’t allow hotlinking, since bandwidth costs them money.