The most interesting thing of their usage is how they managed to create almost realtime search on Craigslist by using Sphinx's delta indexes. And they are doing

The most interesting thing of their usage is how they managed to create almost realtime search on Craigslist by using Sphinx's delta indexes. And they are doing this on lots of data, which is a good sign. Sphinx 1.x+ should feature realtime index updates, which will make the Sphinx deal a lot more impressive. This all said, the support of realtime index updates in the current search engines is a joke and one must do lots of hacks in order to support them properly and on lots of data/updates.