Valid question. I've been building Rails apps since 2006 and since then I spent about 1 month per year on code optimization (not scaling or caching). I'm sure you can easily find people with even more Rails experience, but there're only a few who spent as much time optimizing. I simply enjoy that process more than most people.
I contributed performance patches to Rails (2.x). I created ruby GC patch for memory profiling and wrote memory profiling support in ruby-prof. I presented twice at RailsConf and once on PGCon (on performance). There're more blog posts with performance-related advice from me here: http://www.acunote.com/blog