Reply to Mix length

I've done my fair share of mix tapes, but I'm curious on what's the preferred length. I started recording 1 hour mixes, then 30 minutes, and 2 hours, but now I'm doing 80 minute mixes so they fit on CDs. 2 hours is too long for a mix. I don't believe that anyone ever listens to long ass mixes. I'm pretty sure that 30 minute mixes are most popular. Anyways,
how long are your mixes?
what length do you prefer listening to?