I did a talk about measuring site performance at Sitecore Symposium this year. It seemed to go pretty well, I think:
A collection of people have asked me if they could have access to the slides, and I'm pleased to say you can. Just download them from here:
It's a 140mb PowerPoint file though, as it includes a fair bit of video. It should play on a recent Windows build with the default codecs – but I've not tested it anywhere else than my laptop, so YMMV.
It also includes a full transcript of what I said in the speaker notes – so you get all of the slides, demos and words from my session.