Before coming back to graduate school I worked a few years and during my time in college, I worked as well. I've had my share of good bosses, and not so good bosses as well.
When I was in college I worked a job I really didn't like, but that got me good work experience in the field of study in which I was pursuing my undergraduate degree. My boss at that job was, well let's say less than fantastic. I had a lot going on health-wise when I was working that job and got little understanding from my boss that I was a person with issues beyond just working my little job.
The job just wasn't that important to me, I'll admit, and it was beyond frustrating to have a boss who didn't care about me as a person.
Granted, I know my boss is just my boss, that they really do not have an obligation to care about me beyond what I do at work, but it makes life so much better when they do. When I worked for a couple of years for an attorney right before I came back to graduate school, I got an example of the kind of boss I hope to be one day.
The man I worked for was gracious about employees having to take the day off for appointments, or sick kids. He didn't mind (within reason) if that needed to happen. He had a simple rule, just let him know if you were going to be out of work a week or so in advance.
This is the way I want to be when I "grow up". I want to see my employees as people who are more than just employees. I want to remember that my employees have lives outside of the office, that they have families, and obligations that take up their time and that work is not always the most important thing they have on their agenda. Employees are people too.
I learned that from working for bosses that sucked, and from bosses that were awesome. Even the awesome bosses had their days were I thought, "man I don't want to work here anymore!" But in the end, the flexibility of knowing I could always take a day off if I really needed to without fearing for my job meant something. It meant something to know that I would always have a job even if I took a sick day.
So, remember when looking for a boss look for one who is kind enough to say, "oh you need a sick day? Okay". Those bosses do exist, but if you happen to get someone who is horrible, remember, it doesn't have to last forever and you can always move on. Some things are more important than careers, like sanity.