My previous employer was a 24x7x365 manufacturing company and I was part of the rotating call schedule. The plant at which I worked was actually owned by 2 companies while I worked there. The first company, which treated employees well, was, unfortunately, the Enron of the industry and went bankrupt. This company understood what was mission-critical so the time on call was fairly uneventful, you only were called when product could not be made, shipped, or invoiced because of a computer issue. My boss was also very flexible (he was on the call schedule as well) so that any hours spent working after hours was unofficially granted to us a comp time within the department. This continued when we changed companies for out department. The second company treated and still treats employees, especially exempt employees, as slaves. If they can't get their email from home at 6 am Sunday morning then you had to fix the problem, even if the problem was with their ISP! Needless to say not many members of the IT staff stayed with this company. Out of 9 employees on the IT staff, 5 were "downsized" and 3 left the company of their own volition because of working conditions.

My opinion is that my salary is for ~40 hours per week and when I hit that threshold I should be compensated somehow. Whether with comp time or overtime pay or a raise to acknowledge the extra hours I work. I also know that if I my code has a bug that is stopping the company from working I'll work as long as necessary to fix it and not expect anything for it.