This presentation was held in danish (the slides are in danish, so beware!) at the Umbraco DK Festival on November 19, 2010.
It’s mainly focused on a small set of optimizations you can apply, to get rid of some of the (in XSLT) often unnecessary
if and choose logic, scattered throughout your (no, of course not in not your) XSLT files.
I also mentioned the concept of my "_MediaHelper.xslt" file, which I write about in the “Include or Import” article over here.