I have been using Ableton Live 5 for 2 years and it is very good fun. It's a different way of recording to other systems, like cubase, logic etc... (Although you can still record linearly in the alternative view by pressing tab). If you are good at working in phrases and creating rhythms then it's ideal, as once a loop is created, it can be brought in and out all over the place.
it's best feature though, as it suggests, is the ability to perform live, by creating backing tracks, or if you are a DJ, mixing on it is easy. You have to get used to what all the buttons actually mean, but if you have a MIDI controller, then Live comes into it's own as a live tool. You can control pretty much everything- Playing individual phrases, changing tempo, and adjusting parameters of absolutely everything in effects units and the mixer.
I find it good fun in the studio just sitting there playing with it for ages. If you want a program that is purely for recording though, you may find that Logic or Pro Tools, the more linear based recorders, make your work flow quicker. I'm currently looking into it myself- but there's no doubt that the abilities of Live make for a lot of creative recording!
