I've been messing with the Live5 demo lately. In terms of general capabilities, these two programs are very similar. They both have an arrange view that operates with loops and runs a bit like ACID, have a Live performance view that's grid-based for triggering loops, can record audio, have very solid engines, come with a bunch of synths and effects, are somewhat geared towards electronic/popular music, run vst's and rewire.
P5 comes with better synths in my opinion. Dimension is just awesome and a great value, and PSYN is good. Live comes with a basic sampler and its main synth, Operator costs something like $150 extra (no thanks).
Live seems to have more features overall though. Things that P5 is missing that Live has are things like good bussing options, good Rewire integration with Reason (huge one for me), more audio editing features, both spline and graph automation editing, multiple output channels and multitrack recording, a mixer view...and that's all I can think of right now.
I'm finding Live harder to wrap my head around than P5 was. I thought P5 was amazingly easy and simple to learn. P5's interface looks much nicer in my opinion also.
Live can't run DX plugs, just VST's
. All my nice Cakewalk plugs from Sonar and P5 won't run in Live. Blah.
I've been considering getting Live myself. Currently I'm doing this weird jumping and rewiring between Acid, P5, and Reason and its so disorganized and heavy on the CPU, its really slowing me down. Live's features for me, seem like it would let me consolidate what I want P5 and Acid for into one program: Live, and then rewire Reason in.