Kirk Pepperdine is a primary contributor to javaperformancetuning.com, which is widely regarded as the premier site for Java performance tuning information.
In this interview, he provides advice on many areas related to Java Performance, including why you shouldn't trust performance tips, and the issues with Dumb vs. Complex Code best summed up in his following quote:
"Because we're trained to look at code, when something goes wrong, we look at code... Developers often fix things that have little or no impact on overall performance. I've seen teams literally waste months rewriting ugly code that had no impact on performance."
Read Kirk's entire interview on Java Performance Tuning: