D.T.
OH YES! My daughter is 2 1/2 and I STILL feel guilt very often that I'm working and she's in preschool. She has THRIVED since being in school and loves it, but I still have that guilt. In fact, just yesterday, I was watching her on her preschool's webcams and almost started to cry. They were singing some song and she was doing the hand movements to the song... It nearly killed me.
So, yes, I think all working mothers feel some level of guilt/inadequacy for being away from our kids for any period of time. However, I know that my daughter is well cared-for, is learning and growing and I'm a more content person doing the work that I love.