I have a permanent contract for 0.5 FTE, but am "commissioned in" on a freelance basis for my remaining 0.5+. The upshot of this is that I work full-time with overtime, but only have formal part-time "benefits" (my maternity pay is based on my permanent 0.5, for example). 
As I am a specialist in a small team that focuses on major projects with tight deadlines in an environment with poor workflow management (which is innate to the institution I work within and will never change; they commission my department at the very last minute), I end up working stupid hours (12 hour days are common) and I can get very stressed.
No matter what I do, I cannot balance my workflow because of the federal nature of the institution and its departments, and I have burnt out about four times in the last eight years. One of the problems is that I can't really afford to have an "off-day"; I need to be cerebrally at 90 percent or above on a daily basis to solve the never-ending stream of new problems that need solutions.
The positive side to all this, and the reason I have not left, is that I have an incredible amount of freedom and creativity in my job. So long as I produce something "good", I can go about that production in which ever way I want.
I also have a lot of freedom in terms of working from home and the hours I spend in the office. I really get on with my main colleague, and I am totally accepted for the rather non-conventional person I am.
That latter point is really rather important to me, to be honest. I have worked in more hardcore corporate mentality environments and it just doesn't work.
That said, I am under-paid for what I do. If my boss had to commission an external agency to do my work, he would have to pay a good 75% more than he pays me in salary.
It's a compromise. Sometimes, it feels like my work takes the piss; sometimes, it doesn't so much.