most lcd's i've checked have theoretical viewing angles, but in practice these may wildly differ from the specs
i've been playing some mame on a philips 190s, supposedly a slow monitor, but it looks fine, and is very suitable for single player stand up playing
with a base resolution of 1280x1024 the filters of mame work fairly well, approaching the actual view of a real arcade monitor, but yes, it's emulated so not perfect :-)
i had to smile looking at the arcadevga card claiming to be sharper, yes, i am going to buy one (may get my hands on some elo arcade touchscreen one of these days) but i feel a bit funny about it: people liked the original arcade monitors because they were somewhat blurry, and now we complain about modern 3d cards as they 'soften' the edges...
anyway, most screens i've checked allowed a viewing angle of roughly 45 to the left, to the right, and to the bottom, and perhaps 15 or so to the top, so it just may work, though you may be headbutting your opponent now and again :-)
the biggest problem i
found suspect with lcd's is that when you lean back (on a coctail) the image dims which may be less comfortable on a coctail
however, lcd's are getting better and better, and i'm pretty sure that using a widescreen lcd in a coctail is going to look awesome and pretty usable too! (as those televisions are designed for larger angle viewing, and the 'enlarged' x-axes (rotated to y, obviously) may provide more screen estate to have more fun in face to face coctail mode)
so... who's going to be the first to use a cheap lcd television and put it in a coctail? (gimme the money and i'll try :-))