Here are some topics that CELF member companies have worked on:
Measuring memory accurately
It is important to measure memory usage accurately, in order to handle low-memory conditions better.
Here are some topics of interest to CELF member companies, that don't appear in other sections of this wiki:
Code relocation for better cache performance
See this post by Ingo Molnar: http://groups.google.com/group/linux.kernel/msg/dec15ea546753958?hl=en&
Difficulty of measuring performance impact of size reductions
See this post by Linus Torvalds: http://groups.google.com/group/linux.kernel/msg/e1f9f579a946333e?hl=en&