I never used my playpen for my DS1, but in a sense my whole livingroom was the playpen. The entries to the room were gated off and the whole room was babyproof, so I could leave him in there.
With my DS2, I had the playpen set up in the livingroom and I used the changing table part rather than go upstairs for every diaper change. I also used the basinet to lay him in to play for a few minutes or to take the dog for a walk.
With my DS3, I use it a LOT -- like a cage to protect him from DS2. I put DS3 in his bouncy seat, put the bouncy seat in the bottom part of the playpen, then close the changing table part and basinet part so he is completely enclosed. I hate this -- but if I need to shower or make phone calls this is the only safe spot for him.
Also, I only used the playpen/paknplay for travel sleep with DS1 as neither DS2 nor DS3 slept well in it. :?