Most engine wear is at the top end and comes from lack of oil for the first couple of seconds of not having enough oil. Over time of course this adds up. So the faster the oil gets to the top, the better, hence the very thin oil, "0W". Once the oil heats up, it'll thicken up to "40". It's sort of the best of both worlds. I am sure there is some fuel savings to be gained, but I think for the FSS cars, it has more to do with preventing any premature engine wear due to extended oil change intervals. Of course this "0W" can only be obtained with synthetic oil, at least right now. Porsches come factory filled with 0W-40.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section