Flush Draws

[SirFWALGMan]

I am wondering how to play a flush draw in NL. Now I know a flush draw is almost worthless in NL, because it costs too much to see it to the river. But if the table is passive, and it costs me .50 to see the flop, and then possibly 1-4$ to see the next card or two, is it not worth it? I have won some MAJOR pots at $25 NL with flushes. Usually playing the flush only costs me .50, and I cannot tell you how many times people have ignored the flush on the board and called my 5-10$ raise at the river. Am I playing these wrong and getting lucky? I ask because I always get yelled at when I make these. The number of XXX's I see are way out of proportion to how bad this looks to me, but maybe I am just getting lucky. How bad of a play is this?