i played with this idea with the now-famous wii-mote whiteboard technique, with a view to maybe using it live or in studio if it worked. you do need an IR pen to use it so not strictly touch-screen, but with the gui scaling up a bit you can easily convert any monitor to be a mixer and no doubt the pen approach may be handy in other situations, editing etc. with refining it could work well. most use so far has been using `mspaint` with a pen with my nephews and niece. accuracy is good. i also played with having a set screen layout so the touch screen could just a piece of perspex or any surface once calibrated to be the 'screen'. you could then mark that with areas that correspond to faders or buttons etc. and use that. main benefits include cheapness, wirelessness and ability to convert anything to be touch screen. getting the bluetooth connection sorted can be a pain but no more than a CS & midi stuff etc. requirements are a wiimote, bluetooth connection on you pc/mac, the wiimote whiteboard software (available all over the place) and an IR pen, diy (or u can buy).