[nicky g]

Some random thoughts of mine. I'm way out of nl cash practice, so if anyone wants to correct me be my guest; this is as much to get my own thoughts straight as to offer advice. Anyway, assuming no limit cash:

"are you looking at the # of callers to make your decision, or are you looking toward the pot as a reference."

Start with the pot. If you have actual pot odds to draw, then of course you should call. This happens a lot in small online games, where people make absurd bets (eg 50c into a $10 pot_) etc, or even raise if you think they're likely to fold. Against decent players, they will usually overbet the pot giving you nothing like the pot odds to call. In which case, you have to consider other things such as the number of players and your implied odds.

One player will do if you know he'll pay you off when you make your hand. Implied odds are usually what you're after - ie how much you'll win if you make the hand. This makes your play very player dependant - if you catch your suit, will he pay you off? How does he see you? Do you both have enough money left to give you implied odds? Against poor players, drawing can be very profitable, as they'll often make small, meek bets, but call often ones. But against reasonable competition, you usually won't get the implied odds to call with a straight or flush draw alone.

Against multiple players, you really want the nut flush draw, as if you make a non-nut flush you may well lose your stack to someone with the nut flush. The benefit of multiple callers is that someone else is more likely to have hit something good as well, so if you make your (hopefully nut) draw, you're more likely to find someone to pay you off.
A couple of writers point out that a straight draw can be more deceptive than a flush draw, as it's less obvious when you hit it. Disguised hands obviously have much better implied odds, which is why a set can be more profitable than a better hand such as a flush (though people may suspect a set if you're playing strongly on a ragged board, whereas they might put you on a weak hand or a draw on a coordinated board). Of course if you notice that people are folding when the third flush card hits for fear you've hit your flush, you can start bluffing instead of drawing. If they blithely call regardless of what hits, then you draw instead of bluffing. With straight draws, this can be quite important - in a wild, loose game, drawing to a straight on a tw- flush board isn't a great idea, as two of the cards that make your straight may make someone else a flush, and you won't know where you stand. In a more cautious game, it can be a bonus, as ideally you might be able to bluff the flush if a flush card hits, while they may not notice you hitting the straight (admittedly an optimistic scenario).

Good book: pot limit and no limit poker by Stewart Reuben and Bob Ciaffone. Starting Out in Poker by Stewart Reuben's good for beginners (covers limit, pot limit and no limit).