In our presentations to potential investors, we are often asked to compare PubSub to other services. The third-party grabPerf data makes it pretty easy for us to establish that we're the "Fastest Search Engine on the Web." But, the conversation often moves to a discussion of the highly focused alerting provided by various domain-specific sites. Fortunately, EBay often comes up as an example and we're able to quickly point out just how slow their alerts are. They, like most implementors of alerts seem to have implemented their system using "repeated retrospective" techniques that result in terribly slow delivery of alerts. As a result, we typically see EBay "new auction" alerts arrive days after an auction begins. If EBay were using prospective technology -- like what we provide at PubSub.com -- it is likely that the latency on alerts would be measured in seconds or minutes -- not days.
The EBay alert on the right gives a great example of what happens when you try to use repeated retrospective search as the means of implementing a prospective search application. (Click image to see full size) EBay sent this alert on 12-Sep-2005. However, the auction that it announces expired five days earlier on 7-Sep-2005... That's typical of "retrospective" search implementations! EBay is telling people what past events they missed. Unfortunately, subscribers to their service are probably much more interested in finding out what which future events they can avoid missing.