Can you guys help me understand what response time numbers really mean? I've been monitoring a few different hosts and I see averages of about 304.24 ms on one and 731.78 ms on another. Yet I find that when I actually visit the sites being monitored the 731.78 ms site sometimes loads faster than the site with the faster average response time. How reliable is that metric and is it something you should use?
It really depends on how it's being generated... For example using Pingdom the response times from checks around the world are averaged to come up with the response times and any networking issues between your server and any of the check points could cause the average to go up for one simple example.
If you want a real test of the server's responsiveness, I'd do some testing from one location to another (not several) over a period of time and see how that number fluctuates as it will help to rule out some of the variables.
Uptime checker's response time reports can be helpful, but I wouldn't rely on them as golden.