My company has an official comp time policy, and it sucks. You have to work an extra 8 hours in a week before you can start accruing. After 48 hours, you can accrue up to a maximum of 9 hours (so if you work 57 hours, you get 9 hours of comp time). If you work 47-48 hours every week, you'll never accrue any comp time. I don't like unpaid overtime, but I could stomach that much. However, the part that annoys me is that 9 hours is the maximum, period. Doesn't matter if you have to work week after week of unpaid overtime, you're still only allowed a max of 9 hours comp time.
If you use it up, you can get back up to 9 (again, after 8 hours unpaid each week you accrue). We do get it paid out at the end of the FY if you haven't used it. All 9 hours, if you've got 'em.