One thing that I learned from him and have never forgotten is that you can reduce a harddisk (the spindle kind) performance just by screaming at it https://www.youtube.com/watch?v=tDacjrSCeq4
This is awesome! Reminds me of how "IBM Tech Uses Hard Drives to Predict Earthquakes" [1]. And then it's just one guy screaming at the HDDs.
Yup that is what Brendan is famous/infamous for and it is pretty hilarious. His talks at conferences like say Monitorama are always equal parts amusing and deeply technical. I've been lucky enough to learn a ton from his work on pcc / perf to find a DTrace equiv on Linux.