I was under the impression it checked page retrieval times, which (after subtracting for idle network latency) would reveal which pages were transferring slow b

I was under the impression it checked page retrieval times, which (after subtracting for idle network latency) would reveal which pages were transferring slow because of excess computation or disk use on the server. The idea being if it's slow for one user it's going to be _really_ slow for 1000+. I've not more than installed and tried YSlow once, so I can't say too much about it.