Granted, in the current 'connected' type of environment in which you can be 'in touch' with just about anybody anywhere in the world, there is no such thing as 'private time' anymore. With the advent of technology, with the existence of all types of communication devices and even with so many eyes in the sky, all the science fictions movie might just come true sooner than we expected.
That is why, you must know how to turn yourself off from the office whenever you have had enough. You can do it by not answering calls, being totally out of touch from the internet and even by just drowning yourself in the hustle and bustle of city life.
I was once pride myself being able to be available to most of my clients at any time. I would answer any calls at anytime and in some cases would allow myself to be dragged to the office to finish a certain job. That was before internet is fully utilised like it is today. There was still no Twitter, free teleconference or such things. In this current working environment, only fools would do that as you still can keep in touch with Skype or Google Talk or such other web-based teleconferencing tools.
Nowadays, I usually consider my time outside my office hour is off-limit except if I let it in. Although I love to brainstorm with my partner at anytime of the day, when we say our goodbye for the day, I rarely intrude her space. Unless we have set it beforehand. Usually (if it is over the weekend) there are still a lot of time on Monday.
Maybe our business is not that globalise for us to be able to afford this luxury of private time but should we wait until it is considered as one?