I have last years 3ghz iMac. It takes about 30 minutes to transcode 60 minutes of footage, after it's been copied to a hard drive. Check out digitalheaven.co.uk for their free space calculator widget, very handy for calculating all formats of video vs. hard drive space.
With a 3 year old Mac Pro Quad 3.0 it takes about 30 minutes for 60 minutes of footage for me as well. But this is directly off of a USB 2 card reader. I have tried directly from a faster hard drive and haven't seen that much of a decrease in transcode time.