Just beware blurring the line - it's sometimes first step towards burnout. I wanted to give a reference, here's an article from forbes, http://www.forbes.com/sites/learnvest/2013/04/01/10-signs-yo...

There are studies that show that work preoccupation outside working ours can be a sign of burnout (incoming or undergoing). I know it's great to love your job, that's what flow state is all about, but there can be a darker side to it as well.

Yeah, I understand that. And I do other things to just take a break, even though I find them less interesting then my programming. Also, just to clarify, I spend less time (even lesser than the official time) on the 'official' job that I do. I mostly work on other open source scripts in the free time, which are also helpful for people besides being fun.