In NL Holdem 10 handed most of us are up against 2 cards of the same suit on the flop. What are the odds that at least one player is drawing to that flush. (leaving yourself out). My guess is about 1 in 5. In other words, if you are holding a set or a straight, you will be beat if a 3rd flush card comes on the turn or river 1 in 5 times. (Assuming you don't fill up.)

I assume that most people will play reasonable suited cards that also have other potential. (not 7-2s, t-5s, etc.)

I usually ignore the flush and play my hand accordingly and then pay off or fold if big raise comes in. The odds seem high enough to be a +EV for me.

Very Good.

So about 4 times in 10 at least 1 person would have a flush draw. I think we could safely remove at least 50% of that potential because hands like 2-7s, T-5s, etc. would figure to be mucked pre flop. Therefore about 1 in 5 times would be close.