You can't rest too much. That's my general theory on the taper, though it does come with a caveat. Or, at least, an assumption: that you've been training your ass off for months. And I more or less have, capped last week with my biggest seven-day mileage ever, a lovely 80. There were two 18-milers, a 12, two 10s, a seven and a five. Damn. That's almost real-runner territory. The last run of the week, one of those 18s, was the best. Basically it was broken into three parts, and I went progressively faster, from 8:10 to 7:40 to 7:10 per mile. This was on the mucky, spongy Glendoveer path, which is nice and soft and joint-saving but sucks at least 15 or 20 seconds out of every mile. So those were solid paces for a longish run and better yet, I felt good. This thing tweaked momentarily and that thing served brief notice. But there's always going to be this thing or that thing, at least for me. With increased mileage I've been walking the scary-thin injury line the last month, but I appear not to have fallen into utter disrepair (that close cousin of utter despair).
I'm going very lightly this week. That's in my taper theory, too: the third-to-last week before the marathon is the single best week to get deep rest. Don't wait until it's too late! Deep rest now, then ratchet things up a bit in the second-to-last week in order not to lose fitness, then some short, up-tempo stuff in the days before the race to keep rust from accumulating…. Hey, it's worked for me. I won't tell you I'm a great marathoner, but I will tell you I've always met or exceeded expectations.