Quick answer: 40 min. and very worth it
Last year DD did her "kindergarten" year in a half-day preschool class for 4 & 5 year olds (she turned 6 In Jan. that school year) and it took us 40 min. to get there from home. This year she will go to a private school just around the corner from preschool where DS will now attend. Since it was such a long drive, DS and I are nomads up in "the big city" and we had a great time. Every day we went to museums, parks, playgrounds, libraries, and a few errands here and there. There were times when we wished we could just stay home, but usually once we got going we enjoyed ourselves.
Regarding the commute itself, the time spent from out-the-door at home to in-the-door at class is *LESS* than the bus ride. We spend the commute time chatting, listening to books on tape/disc, coloring, etc. It's a really great time to chat since you have a captive audience.
I think that will become invaluable as the kids get older.
Regarding playdates -four things.
1.) With longer school days, kids around here do not have after-school playdates much at all.
2.) We keep in touch with the community via a local playgroup and after-school activities.
3.) With a private school & lots of parent-pickups, it makes it easy to have lots of short play dates right on the school grounds. Our public school friends rarely do this, they all take the bus home.
4.) Once you've gotten to know a family, and the kids are old enough, they can go home with a school-friend for a playdate
We joined a local playgroup when DD was 13 months, and have stayed friends with 4 families that we really hit it off with (original playgroup lasted for about 3 years, and consisted of about a dozen families - we still enjoy running into each other at the library, store, etc.). You could also meet local families at the library (many have infant or toddler story times), mom-orientated clubs (Holistic Moms, Moms in Motion, MOMS Club, etc.).
DD & DS did Kindermusik & library story times when they were little, and DD enjoyed a local Lacrosse team this past Spring. This Fall she is signing up for the local hockey team. Our local friends see us outside of school more than they see pretty much any other friends.
Kids spend such a huge amount of their childhood that I think it's so important to send them to the best environment you can manage. Every family has to decide for themselves what their limits are, and what is the best fit.
As for what to do once both kids are in full-day school, I hope to get a job in the area near their school. So we'd all commute together.
Feel free to PM me if you want to chat more.
(p.s. We live in a very good school district, with a large enrollment and lots of great programs - it's just not the educational philosophy that fits with our family.)