That's why, on admit weekends, you make sure and ask grad students where the good places to have fun are. It's not that you need them to actually tell you, it's that you want to make sure that they have an answer other than "there's a nice coffee shop in the bookstore I go to sometimes to work when the lab gets stuffy."
On a more personal note, I spent a summer at U Chicago and the grad students I worked with kept fairly normal 40 hour work weeks. They even took vacations. Now, this is the summer, but I'm willing to give during the school year an extra 20 hrs a week (over the 40 they're paying me for) as time invested in my education. The lab's post-doc came in at 8, left at 4 every day (as did the professor). Maybe it's that my PI was just a really nice guy, or maybe it's astronomy/astrophysics, which is in general a little more collegial than cut-throat (there isn't a huge amount of rat-racing to a result, like there might be in HEP or applied physics).
I work as a high-school teacher now, and I can tell you there are similar responsibilities in hours (60+), for considerably less reward (both financially and mentally), at least initially (lesson planning, grading, lecturing, dealing with parents, etc for 120+ students). That said, I couldn't handle the hours forever, and while I wont mind 60 for the duration of my PhD, once I graduate I'm sure as hell not working many weekends.