I've done both, maple veneer ~0.050" and maple 'drop top' ~0.125" (1/8th). The drop top was infinitely easier, although both were done on a flat top body (no forearm contour or anything like that).
I glued both down with Titebond. With the veneer, in addition to the bookmatching problems Drak mentions, another problem I had was that my glue thickness was not uniform across the body, so I had a whole series of bumps, dips and swales that were subtle, but still there. They would have been accented by the finish, I'm sure. When I flat-sanded the whole thing off, the higher parts sanded thru to the glue before the low parts, confirming my intuition.
Maybe thinner glue, or better clamping, would have done the job better. Best results are probably obtained with a vacuum press (I'm waiting for my wife's vacuum cleaner to fall apart so I can scavenge the motor...)
After the veneer fiasco, I sanded back down to mahogany and applied the 'drop top'; got it lined up and flat in no time. I was able to plane it down with 80 grit on an orbital sander and still have plenty of thickness. I think 1/8" will bend OK as long as you steam it first (follow the tutorial on the 1/4" top). If you go thicker than 1/4" you might have enough thickness to do a carved top.
I've heard that anything thicker than 1/8" will begin to affect the tone.
best of luck