Speaking of Mac Mixing Apps, I hear that Final Scratch and Baytex Party are the bomb.

More specifics on Baytex, courtesy of Bart Cheever, CEO of DFILM:

"Any Mac DJ's out there I *strongly* recommend you check out Baytex Party - by far the best MP3 DJ player on the market, IMO. It's got great features like: Easy to use very natural feeling pitch control, Multiple sound outputs (so you can cue and beatmatch one MP3 while the other is playing), Rock solid - never ever crashes, Simple feature to count and enter BPMs (you can sort your entire MP3 library by BPM). I've tried most of the other MP3 DJ players out there and I haven't been this excited by a product since I bought my original 1200's 17 years ago!"