Read the terms. If you cancel your account for any reason (or they cancel it on you) they will keep any money you have put in your account to pay for swaps or postage.
I've also has some pretty rude customer service from them (the real reason I cancelled). USPS lost a couple of CDs coming to me and the customer service rep accused me of just never marking them received, took extra credits from my account so I ended up with negative credit and told me they won't refund the money left in my account. Not worth the hassle unless you want to trade for a bunch of $1 bin cds.