When freelancing at an hourly rate, I often use that same calculation for everything that I do. That $15 cab ride will save me 20 minutes on the subway, maybe I can figure out a way to work more efficiently and bill that time?

I no longer find the mentality of wanting to make that calculation productive. Treating my time like such a scarce resource makes it hard for me to "waste" my leisure time. My rational self questions why I choose to "lose" 6 hours rock climbing, when it's something I completely love, but had to trade off many other things I could have done.

Similarly, it's a huge reward for me if I can get hired for 40 hours of Android development project that's going to "cost" me an additional 10 hours of un-billable time to be "forced" to learn something that I've wanted to, even if I'm "losing" more than it would have cost me to pay for some Android dev workshop.

I'm in my early 30s and personal time seems to have shrunk. I now cherish grabbing a beer for 45 mins after work with my childhood best friend, because he has kids. When ten years ago we would have thought nothing about wasting hours.

My point is that when I was eager for it, dollars were a great metric for my hourly value. Now, personal enjoyment, or feeling like I'm doing something valuable with that time has a much greater importance.

That's my $0.02.