We now do it routinely for prone GA cases (microdiscectomies, achilles tendon repair, etc).  We also induce in the prone position, with the gurney aside the OR table, and insert the LMA after the patient is asleep.  THe patient is able to tell us if anything is uncomfortable prior to induction so we don't have to worry about nerve stretch or any body part being compressed between the Wilson Frame.  We have had good results, and haven't had to turn the patient supine in any of the approximately 30 cases we've done so far.  We are in an ambulatory surgery center, and it speeds time to prep and incision.  No regurgitation so far, and if they did it would come out their mouth.  It's actually much safer regarding aspiration than the prone position.