I'd be interested to hear from people who have followed this plan to see how they got on with the marathon. I can't help thinking that 16 miles just really isn't enough to get you prepared to run 26.2 as strongly as possible. I know in the blurb they tackle this objection by saying that there is a cumulative fatigue effect of doing back to back "sort-of" long runs, but IMO unless you're running many more miles in one go, I don't think you're doing enough to teach the body to burn fat efficiently. (No doubt glycogen reserves will be slightly depleted when you go out for your Sunday run, but I'm sure between Saturday's run and Sunday's run you will have consumed a fair amount of calories and hopefully had a good night's sleep.)
I do think the back-to-back "Something of Substance" (their terminology, not mine) sessions are a very useful practice to get into, especially if in the long term you're thinking of doing an ultra, but I don't think 10 + 16 miles over a weekend is really enough. Something like the Hal Higdon plans do something similar, i.e. towards the end of his Intermediate II schedule you'll do 10 miles on Saturday including MP, then 20 miles on Sunday. (I pushed it to 22 on my first marathon and topped out at 23/24 since then.)
As well as getting more physically prepared, I also think that getting more miles done in one go will give you more confidence that you can complete the full distance. On the other hand, if you have complete faith in the schedule and know that it has worked for other people, then fair enough. I wouldn't mind seeing the evidence though! 
Edited: 04/11/2011 at 10:47