From No Limit Hold 'em: Theory and Practice by David Sklansky and Ed Miller.
Concept No. 36: Be more apt to slowplay very good hands that aren't quite the nuts than the nuts itself.
This concept seemed wrong to me from the first time I read it, but the authors bring up an interesting point in the discussion. After considering it, I still think the advice is generally wrong.
The point that Sklansky and Miller make is that one of the benefits of slowplaying a hand that is not quite the nuts is that you will potentially save a lot of money if you happen to be up against the nut hand. The example they use is a J66 flop. Here they say you'd rather slowplay with K6 than with JJ, because with K6 you might save money if you are up against JJ, J6, or A6.
Well, this is true, but it's a minor concern because your opponent will so rarely hold one of these hands. In the extremely likely event that your opponent does not hold one of these hands, you should be more apt to slowplay with the nuts (well, JJ is not the nuts, but we can imagine we hold 66). It's possible that there may be some situations where you would save so much money by slowplaying with K6 when you are behind that it actually is correct to slowplay it in a situation where slowplaying with JJ is not correct. However, I think this would be extremely unlikely in practice.
Sklansky and Miller neglect to mention the bad things that can happen when you slowplay. By slowplaying:
1. You don't get as much money in the pot when your opponent would call you.
2. Your opponent might outdraw you with a hand he would have folded.
3. Your opponent might have called on the flop but be scared off by a turn or river card.
4. A turn or river card might scare you enough that you have to stop betting or raising.
Factors 2 and 4 are a much bigger concern if you hold the near-nuts than if you hold the nuts. These problems are relatively common, at least when compared to the likelihood of finding that you're up against JJ when you hold K6 on a J66 flop.