For me, the choice is simple, I'll do what it takes to get the job done so long as management's expectations and goals assume a 40 hour week. I'll work after my 40 hours if to help out as needs so long as their expection and goal hits that mark. If they every give me grief about being a few minutes late due to traffic, etc... but don't pay me for the 20-30 minutes I worked over the day before, we'll have a problem and I'll never work another second over 5o'clock ever again.
Aside from that, they know the law and if they want something done bad enough to tap over 40 hours, they can pay time and a half, or decide that it can wait until tomorrow.
What I cannot imagine is how an employer can reasonably expect someone to work extra without pay except as part of a "lets keep it friendly and I might need you a little late every now and again and you'll want to ditch out a little early now and again and lets not make a federal case over it" mentality. If you had to contract out work to a plumber, per-se you'd instantly assume they would get paid hourly... period. What I understand even less is geeks who work insane hours knowing their company probably considers them at best, a necessary evil, full well knowing that it is the (legal) responsibility of the employer to either fund enough positions to get the hours of service they feel they need to cover, or fully expect to pay when they use the workers post 40 hour free-time.
I feel that if you are setting the employer's expectation that a technician (or whatever) is willing to work 60 hours' for 40's pay, you're harming all the technicans who do want to pursue outside interests on their own time, and when the day comes that you're ready to scale back to 40... you could have painted yourself into a corner.