Bill Burnham thinks it is the next battleground.
Persistent Search allows users to enter a search query just once and then receive constant, near real-time, automatic updates whenever new content that meets their search criteria is published on the web. For example, lets say you are a stock trader and you want to know whenever one of the stocks in your portfolio is mentioned on the web. By using a persistent search query, you can be assured that you will receive a real-time notification whenever one of your stocks is mentioned. Or perhaps you are a teenager who is a rabid fan of a rock group. Wouldnt it be nice to have a constant stream of updates on band gossip, upcoming concerts, and new albums flowing to your mobile phone? Or maybe you are just looking to rent the perfect apartment or buy a specific antique. Wouldnt it be nice to get notified as soon as new items which roughly matched your criteria were listed on the web so that you were able to respond before someone else beat you to the punch? Persistent search makes all of this possible for end users with very little incremental effort.
