I signed up for 6 month. Since the service was pretty dead, and I didn't think it was me, I tried OKCupid after a month and found OKCupid was much more active. Once I started dating exclusively someone I found through OKCupid, I tried to close my accounts.
I had no problem suspending my OK Cupid membership; however, eHarmony would not let me suspend nor stop my membership, so it ran its inactive course for 6 month. I suppose that makes it look like they have more active daters than they actually have, since probably most people move on like I did.