Both of my kids are too drained after school for formal playdates - they sometimes play in the driveway with neighborhood kids, but usually come home and want to veg out.
My 4-year old attends preschool five days a week. He occasionally goes to a neighbor's house on the weekends, but that's it so far.
About once a week, my 6-year old plays with school friends at the park after school for about an hour. That seems to meet his socialization needs.
I am a huge extrovert (and a SAHM) but haven't had a ton of success setting up formal playdates. They play with each other and don't yet crave more, so I am just rolling with it for now.