Earlier quoted context omitted.
Actually, I've tested this. You get 10ms of extra delay per request, not 150. There might be some magic value at which KeepAlive will be helpful during non-peak periods without crippling the server during peak periods, but for a well-engineered site, the extra 10ms delay per request shouldn't be a big enough deal to warrant risking a full-on site outage later on. Also, this has already been discussed to death on HN:…
Light travels less than two thousand miles in 10 ms, and TCP requires three one-way trips before starting the first request on a new connection. Anybody more than 620 miles away (about half a time zone) is guaranteed to have a higher ping time than that.
I was fairly careful with the test(s), and the 10ms difference seemed to be consistent. So that's odd. I need to investigate that further.