Keep in mind the nuts. Drawing to a flush with 87s could be a problem when a higher flush is out there.
However, even more of a problem is drawing to a non-nut straight. JT always makes the nut straight. So if you have something like 76, you need to be careful. A board of 8 5 K is a lot better than a board of 9 8 K (remember JT is out there).
As well, pairing the board brings the possibility of a full house which screws both flushes and straights.
As a final note, when you have an OESD and there are two flush cards on the flop, then potentially your 8 outs for the straight could only be really 6 outs because two of the outs could make somebody a flush.
Here is a good book on limit holdem for the internet:
http://www.amazon.ca/Internet-Texas-Hold...7752&sr=1-3