I'm feeling this pretty strongly as a minimally part-time freelance developer; I can't afford new hardware, and am coding on a machine that was at best a mediocre performer seven years ago. Startup time for fairly trivial applications is significant running Lubuntu, and starting a Clojure app is painful; I just timed Clooj at 1:48.

I find that it affects my decision whether or not to optimize code; I feel it sooner than I remember doing when I was on a more powerful machine, and that makes me decide, "That inner loop has to go." It also affects my choice of language; I'm more likely to use Pascal or Nim than Python, because the result feels better when I run it.