In looking at the REST API, it seems like it wouldn't be that hard to write a bot that crawls the web and indexes services (Map Services, GP Services etc.)
Is anyone already doing this?
Update1: I can find lots of mapservices with simple google search.
I rather doubt google gives a very high ranking to mapservice pages though, so I'd bet there are a lot that are missed. Anyway, if someone were to crawl all these mapservice pages and assemble an index and expose that index on a site. The site could allow me to search for mapservices that are in a particular region and contain certain keywords and add the mapservices to my map. AFAIK the arcgis.com map gallery isn't built by a web crawler.
Update2 With a funcion named MapServiceHarvester, it sure sounds like Richie Carmichael might be cooking something up.