[frappeboy]

If there is a raise on 3rd almost always call 4th in this situation. The only time you don't is when someone pairs their door card (goes without saying), or there are 2 opponents who have scary looking 2 flushes on board higher than your flush draw. Like if one guy had Ac Qc showing and another guy had Jh Th, folding is probably correct especially if these players are yet to act.

As for 5th street, you should usually auto muck unimproved UNLESS everyone folds to you and you can continue heads up against the original bettor. In this case you should seriously continue going to the river since there is so much dead money in the pot. Obviously if your hand is dead or your opponents board is very scary you'll do better off folding, but even if you only have a pair of deuces here and your cards are fairly live you can usually chase.