FTrain:

"Well, computers still aren't listening to us as well as we'd like, but in the meantime the technology matured, and what really happened is that centralized databases - and Amazon and Ebay were prime examples of centralized databases with millions of items each - could suddenly be spread out through the entire web. Everyone could own their little piece of the database, their own part of the puzzle. It was easy to publish the stuff. But the problem was that there was no good way to bring it all together. [...]

That all changed - suprisingly slowly - in late 2004, when with little fanfare, Google introduced three services, Google Marketplace Search, Google Personal Agent, and Google Verification Manager, and a software product, Google Marketplace Manager."