I use Ableton Live 2 and about to get version 3 soon. It is very useful you have rewire support it works with Pro Tools 6, Sonar, Cubase all the premier recording packages. The looping abilities are far greater than Acid (not diminishing what acid can do) but you have the time warp feature which matches up any loop regardless of tempo, pitch, etc and sequences them together nicely. The effects are good, it has VST support so you can use VST's inside of it, you can create some complex arrangements with it. So in my opinion Ableton Live is The Truth! I use it as a sequencer for my sounds and loops and run it in Cubase, oh I can't forget about the ability to play your shit live with a band or whatever save the sessions etc. Must have software tool if you work with loops based recording.