Certainly this is not a bad app for a 1.0 freeware release. But there's still a long way to go.
For now it should be okay for hobby DJs who would like to go slightly beyond iTunes' Party-Shuffle. But if you deejay professionally, don't expect too much at the moment.
I've tested djay on a Powerbook G4/1.67/OS 10.4.6 which I use for deejaying regularly with the DJ-1800 software. Unfortunately djay doesn't run as smooth, especially if you use the Pitch and Tempo. (To be honest here, DJ-1800 needed some time as well to evolve to the rock solid DJ app that it is now...) And don't even try the Maximum Quality setting on a G4... (well, that's no surprise though and it's not djay's fault)
The interface has some good moments as well as some bad.
- iTunes integration is nice. But Artist/Song/Time columns are not enough, I would certainly need BPM/Genre/Year/Album/Comments/Grouping, even Composer as well. And Drag&Drop from iTunes playlists doesn't work, unlike with DJ-1800.
- Artwork is very nice, when it works, that is. And would be even nicer if the images wouldn't be mirrored...
- I don't understand the purpose of the black-to-gray background gradient. It's simply disturbing!
- All functions, sliders and buttons should have their keyboard shortcuts whenever possible: Start, Pause, FF, REW etc.
Hint: If you don't have a 4-channel output device, only a 2-channel iMic or similar, try to group it with the built-in audio I/O to an Aggregate Device using Audio Midi Setup utility. In theory this should work. (I don't have the iMic with me right now so I can't confirm it though.)