This mini review is aimed at people looking for the first time and trying to decide. it is not a detailed test.
In the main, this is a very good app. I have found it very stable on both Tiger and leopard using a (non intel) 1.5Ghz powerbook with 2Gb Ram and a 2Mhz imac. Plus points over several other app's are: 1) it will happily play itunes protected files albeit with some restrictions on processing (e.g.midband control, full e.q. and effects such as delay and reverb)- however, these are not the fault of Disco XT but the nature of protected files. 2) has both a manual mode and fully automated mode. The latter allowing you to set up an auto-fading playlist whilst you the DJ go to get a pint, visit the John or whatever. 3) decent interface with various skins, a couple of things you don't need which thus clog up the page a little, but generally not confusing. 4) well written guide which assumes little or no knowledge.
If you want to use the BPM facility make sure you have a decent mac as this is processor intensive. The whole program used to be pretty processor intensive but is much leaner now.
My only gripe is with support. they're good but can be slow. to get stability with os x 10.5 I needed an update (which should be free) but you have to email them first! With a gig on Saturday, I emailed on the previous Wednesday. It's now monday and have heard nothing (despite a reminder sent). Consequently, I have had to pay again for a full version in order to get the upgrade!! i hope they will refund but first i hope they will reply...
So advice is to keep up with the upgrades even if they are too frequent.
Some people on this forum have been recommending DJay. I initially rejected it because it appeared to lack an auto feature but I was wrong! Playing with it now it's really rather nice....