I don't know exactly how to describe the feeling, and I feel like a spoiled brat or a wimp for even having it, but I'm basically talking about that kind of bored feeling of waiting for the day to be over, killing time, trying to think of a good reason to leave work early, etc. I mean the basic feeling of just not wanting to be at work.
It turns out to be true that grad school, for me, totally does not have this feeling. I had it over the summer when I worked in the math lab (a worse job than any I've had in many years, though still not bad in the overall scheme of possible jobs), but I don't have it during the regular semesters at all.
It's interesting. I spend more hours at school now than I ever have at a job, and (more or less completely independently) more hours working than when I had a job. But I simply do not have that feeling of being required to be in a place for 8-9 hours every day. Aside from my office hours (4 per week), I am always either doing a specific thing (teaching or attending class or a seminar) or I am free to go if I want to. Everything now is about accomplishing specific tasks on time rather than spending a particular amount of time appearing to work.
Consequently, my office, and the building where I work, doesn't feel like a workplace to me. It feels a lot like my dorm felt when I was originally in undergrad, actually - like a cool place to hang out, the place where I do most of my work, and the place where, at all hours of the day and night, some of my friends and acquaintances are around.
I was able to confirm this when I was working in the math lab. I left there one day during my shift to go to the restroom, and when I walked out into the hall, past the offices of my friends, I had a feeling like, "Oh, I am trapped in the math lab, and all these people out here get to have their regular lives."
That dreadful feeling of being trapped at work was a really large feature of my previous life, and it's pretty fantastic for me that I don't have it anymore. It's like, as I wrote once before, my work life and life life have all become the same thing. Some people hate that aspect of grad school but I think, for the most part, I really like it.