DJ-1800 is a somewhat nice application, but have perfomance problems as do competitor Disco. Both DJ-1800 2.2.1 and Disco 2.8.9 gave Audio dropouts both when I loaded the second track to play and in Disco also when I momentarily switched applications. How's that for a nice first encounter? This was on a 400Mhz Powerbook G4 that otherwise run Traktor DJ Studio 2.6.2 as well as Traktor Beatport 1.0 very well. In addition Traktor *sounds better*. It has its own audio engine which helps. AFAIK both Disco and DJ-1800 rely on Quicktime. I have QT 7 on Mac OS X 10.3.9
 
Both Disco and DJ-1800 should be compared to the free Traktor Beatport application (you'll need to register, which is free) as well as the professional Traktor Dj Studio suite. Both Traktor versions outperforms DJ-1800, though DJ-1800 have more features. I haven't tried Traktor Beatport on G3 hardware though, nor have I tried Traktor DJ Studio 3.
Even the free Traktor Beatport have keyboard shortcuts, which really helps. Where are these in Disco and DJ-1800? Big plus for Hardware support in DJ-1800 though!!!
 
DJ-1800 has a few pluses over Disco as you can precue in many decks (Traktor Beatport also only have 2 decks) and better performance IMHO even on older hardware. But in an audio application, audio dropouts are unforgiveable. This Traktor DJ Studio also had before version 2.6 and I told them the same thing back then. Native Instruments listened. Traktor rules!
If you can't afford the real Traktor, even second hand, do yourself a favour and check out Traktor Beatport as well as the alternatives. Use what works for you! For G3 hardware DJ-1800 may work best, but on a G4 Traktor Beatport should convince. There are also a number of new features in DJ-1800 2.2.x that may tip the scale for you, so make sure you check them all before you decide.
Real-time apps are hard work, but if you can't outcreate a free application you might as well develop something else. I suggest both developers (of Disco and DJ-1800) try and improve their apps beyond Traktor Beatport. It sets a standard any DJ app should meet or exceed. Right now, it seems DJ-1800 could very well do that in a future incarnation. But the audio dropouts just have to go. It'd be better to have the interface freeze rather than the music.