I take a single Motif 6 keyboard to play live gigs. Now let me think, I could replace that with a controller keyboard, plus a laptop, plus an extra stand to put the laptop on, MIDI cables to connect them together, then hope the D/A circuitry on the laptop compares with the Yamaha Motif, hope that Windows doesn't crash ( which has happened to me on numerous occasions even when only running Microsoft software let alone 3rd party software ... my Motif has NEVER crashed ), plus the inconvenience of changing patches through MIDI. Hey don't get me wrong I think software synthesis is an awesome innovation and and can provide excellent value and performance but I much prefer to use hardware synths and FX on a live stage just for reliability. A project studio is another thing entirely and computer based synthesis and DSP processing can't be beaten. But I will still be buying dedicated synths for live playing.
I have been making my living programming computers for 20 years now and know what computers are capable of which is exactly why I don't rely on them on the road. Sure the day will come when I will use them at a live gig but not without having a hardware synth to fall back on when something goes wrong.
It depends a lot on your situation. Maybe if you are playing mainly preprocessed dance music you could get away with just a computer but even then I would think you would still need at least a control surface for live input plus a backup computer in case of problems.
[This message has been edited by Nigel (edited 04-20-2005).]