brmmbrmm - 9:18 am on Mar 4, 2004 (gmt 0)
The "proof" for one of these came when I adjusted the ALT tags to use different ones for each image. After just a few days and several Googlebot visits, a site that had been out of Google on any relevant search (all relevant search terms had been in the ALT tags) was back for just one relevant search. Yet a slightly more relevant search showed nothing. I noticed that the phrase that was now working was the only one where no ALT tag included those words.