Comp Time was discussed between our union and employer at one time, but they weren't sure if federal laws would allow it. Most of the workers were in favor as long as the paid time off was going be equal to the overtime pay. Meaning that you'd get 1 1/2 hour off for each hour of overtime, which the company had no problem with.
On the plus side, our company doesn't have a problem with taking unpaid time off, but it would be nice to be able to bank overtime pay to cover it. Then there is the fact that overtime sometime bumps you into the higher tax bracket for for a pay period.