There's a race every year called the Euro Marathon that's part of the Lake Geneva Marathon Events. It was supposed to be this past weekend (5/11/13) but sounds like it was cancelled. The FKT from the historical race results appears to belong to Matthew Krump from 2011 who ran a 2:18:40 (6:19 pace). I've run this a couple times, once with my wife and once this past winter in the snow. It is truly unique and beautiful, in a man-made sort of way. If you get a chance to do it, I would recommend it.
I did this run over the weekend and was blown away by how fun it is. Any trail runner living near this area should definitely run this path. I don't think you'll find another 21-mile stretch anywhere with so much variability of surfaces to run on (from cement to crushed gravel to dirt to grass and every other surface in between), and I was surprised at how so much of the trail felt like it was truly in the woods, with no houses in sight. Of course, the real highlight is getting a sneak-peek into the lives of the rich and famous in their multimillion dollar mansions. I did the run in a leisurely 3:42 and came back the next day to re-do some of the highlights. Here's an outline of the route: www.usatf.org/routes/view.asp?rID=429326.
Also, I can't believe the powers-that-be actually allowed a race to happen along that trail...phubbard, do you have any idea why it was cancelled? I'd definitely do it next year if they put it on again.