I have a swing and I love love love it!
As for how much....as Olivia is only waking once in the night now (woo!) I tend to pump the other side when I wake up to keep my supply up, and to stop the fullness. I'd say on average I get 4oz out of it.
It takes a bit of practice, but the main thing for me was to find the best position for your nipple inside the pump bit, and the best suction power for the initial quick sucky bit. Also switching to the slower suction as soon as you see those first drops of milk.
My freezer looks really healthy..now I've just got to try and make her take a bottle

xxxx