Last week I got to analyze a web page that spent 4.8 seconds in the onLoad event handler of a custom script file. It turned out that 2.8 seconds were consumed by applying a dynamic menu library. The remaining 2 seconds were spent in jQuery selectors. The analysis showed that most of the selectors didn’t return any object and those that returned objects can be improved by using different selectors.
Read the full analysis and a comparison between different selector types at 101 on jQuery Selector Performance