With jQuery 1.3.2 out the door I've been looking for more ways to profile and optimize jQuery. Previously I did a survey of jQuery-using sites to figure out which selectors they were using. This led to the construction of the new Sizzle Selector Engine which targeted those selectors for improvement. Additionally, I constructed a deep profiling plugin for jQuery which helped to spot methods that were taking a long time to run in live jQuery sites. This helped bring about the improvements in jQuery 1.2.6, 1.3, and 1.3.2.
Programatically profile functions, allowing you to analyse the output easily and pinpoint bottlenecks.