Performance: we wish the incentives were there to focus on it more often.
Lars would like more opportunities and incentives to focus on making things fast, rather than just making them not slow. Unfortunately, things tend to line up so that fast enough and more features are in focus. Plus, performance and optimization can be very context sensitive and age out without anyone really noticing.
Also pondered: IRC, Gentoo, and the eldritch horrors buried within the x86 architecture.