I always figured that if I wanted something, or I was asked something, that didn't quite fit in with normal arrangements an easy way to see if it was reasonable was to see if the flipside would work just as well.

So if I needed to work late to fix something specific I'd do it gladly, as long as my manager was the type who would let me knock off early if I had a specific requirement (the flipside to that was that I'd only knock off early if I were willing to work late when required).

If I was suddenly told that I was expected to work late every night for a month to get a project back on track (like the time I was given a document in October for a "critical" project but the document was dated April), I refused on the basis my manager would never have let me leave early every day for a month. That particular case also highlighted mismanagement - as I pointed out someone had sat on it for six months so if it had become urgent the failings had to be acknowledged.

There's a difference between being a jobsworth and being a professional. There's also a difference between being a professional and being a doormat. In my mind a professional will get things done but will also have enough self-respect that an unscrupulous manager won't get to take advantage of their professional goodwill.