Education time for me...trade etiquette

Hello all, have a question for all my fellow traders out there.  When do you consider a trade "dead"?  How long do you wait for someone to respond to you before you assume that the trade that you have offered, or is in progress, is no more?  The reason I ask is because I'm not too sure what is acceptable etiquette in these cases, and I surely don't want to piss a potential/current trading partner off by assuming that he/she is not going to contact me about a trade anymore (and thus offering the cards in that trade to someone else). 

2 days, 1 week, 2 weeks?  Help a brother out here folks, tell me what you believe is the proper length of time to wait before considering a trade dead.  Hope to hear from you all soon...thanks,