I did use a demo of ejay a few years ago - haven't heard anything of it for a long time though, so I hope this isn't too outdated!
It was quite good, actually, though in some ways rather limited. Basically, you have a set of eight tracks which you can fill by dragging and dropping any .wav file from the considerable library. You could also load custom audio clips to provide your own sound effects/audio loops.
It was a bit tricky settng up a continuous drum beat - the components were often very short, no more than a couple of seconds, and you had to manually extend it for as long as you wanted it to be (don't think there were copy and paste features).
As a music editor, you're limited to the audio samples in the libraries (they were divided into Rave, Hip-Hop and Dance, but you couldn't, for example, access Hip-Hop elements when in the Dance editor, which was a little irritating.) All in all, it was great for a beginner, who wanted to write music by arranging the pre-recorded samples. To write your own music, though, you'd probably need something else. It all depends just what you're after.
Hope this is of some use, although as I said I haven't worked with ejay for quite some time!
"I wish I was a spaceman, the fastest guy alive. I'd fly you round the universe, in Fireball XL5..."
