I'm negotiating part time working at the moment and I've asked for 4 short days. I really found in my office if you weren't physically there you lost a lot of influence. So much of the job is about building and managing relationships, rather than just sitting at your desk cranking work out.
It would be nice to work only 2 or 3 days, but I think I would struggle in the office, even though I'd be having a nice time with the kids.
Also on a related note, to make myself feel less guilty, one colleague went straight back to work after her children were born. But then took a 5yr career break to help them through gcse's and a-levels, now all dc are at Cambridge!
Just interested in everyone's thoughts about how to make it work.