It depends on your machine. "All day" is normal speeds for G4s, or even G5s.
What are you running?
What OS?
What Processor(s)?
How much RAM?
And why are you using Popcorn? What's wrong with Handbrake?
As wmealer pointed out, this is a hardware issue. Encoding video is very processor intensive -- here's a case where the more horsepower, the better.
Before I upgraded hardware, it could take up to 7 hours to encode a DVD.