Speaking for my experience...I am usually the one not cumming during play time. My SO is usually a tough nut to crack anyway (it generally takes him a while to get there when we are having sex)...eh, not too much of a pun intended there.
I mean, things are feeling really good...but of the few swaps we've done, I've had one orgasm from a play partner (and I'll say it was very good facelick ). We're going to a party this weekend...I'll see if my luck improves...lol
Maria