In the section "When Not to Semibluff," Sklansky mentions that semibluffing when you're last to act (and no one has yet bet) is generally not a good idea, because you run the risk of being checkraised. Let's look at why:
It's the turn, three players still in, the pot is currently 3 big bets, it's checked to you, and you bet with a flush draw, on the button. This is a bad idea (unless the table is one where the two other people have shown tendencies to fold too often, not a common scenario at lower limits), and there are many reasons why:
1) You're betting as last to act. This is - even by very weak players - seen as a possible attempt to steal. Your bet on the button is less intimidating than you may want it to seem. This lowers the chance of a semibluff to work. This is mostly a sidenote, though, and the real problem lies in:
2) If you're checkraised, you're getting a clear indication that you're going to see a showdown, i.e. you're not going to be able to bluff the checkraiser out of the pot on the river. You now HAVE to hit your flush to win. What's worse, you're only 20% to pull this off, which means that now you've invested 2 big bets in a pot (because you have to call him, the pot is laying you too big odds not to) where you only have 20%
equity. You just lost 0.6BB immediately by betting, and the checkraise gives you a chance to lose 0.6BB more (to quote Sklansky, "do you see why?"). Folding, of course, is even worse; now that you've made the pot big enough, you're getting 6-1 on your money, and folding means you forfeit equity worth 0.2*6 = 1.2BB. You lose money by calling and you lose money by folding. Raising is the worst option, of course.
This brings us to another point that is brought up in another book (at this point, I can't remember if it's Small Stakes Hold 'em or Hold 'em Poker for Advanced Players): It's more devastating to get checkraised with outs, than without outs. Let's look at an example of that:
If you hold JJ on a K-T-4-T board. You're on the button, and you have a caller. You bet again on the turn, and now he checkraises you. You can happily lay your hand down. If you're behind here (which you always are, barring bluffs), you have only two outs. You're sacrificing very little equity by folding.
On the other hand, if you had had QJ and gotten checkraised, you would suddenly have found yourself in a dilemma similar to the one above, where you WISH you had checked, but didn't.
So, in conclusion: If you have outs, check behind. If you have no outs, bet. "Having outs" means "several outs", having "no outs" means 3 or less, but it varies.