In viewing the time to first byte, we get some insight into the time the web server takes to process a request from a given location and connection speed, and perhaps how much network latency is factoring into the round trip to the server and back (which is, as Ilya Grigorik kindly points out, the web’s current performance bottleneck).
Lot’s of solid performance advice in here as well an interesting look at the recent Wired website redesign and how a few small changes can significantly improve perceived web performance.