Not because of leaving the baby (although that has its own challenges), but because it is both hard to get caught up and humbling to realize that things moved just fine without you!
I am petty, but I will say that I am glad that there are a couple of projects that basically fell apart when I was gone. It makes me feel like me being gone actually had some impact.
Re: Going back to work is hard!
I spent weeks putting together an email with all the things that need to get done while I am gone, as well as issues that may come up and how to resolve them, I put a lot of work into this email...NOTHING got done while I was gone, nothing! I was not happy. And when I mentioned the email to my supervisor (who had gone to another office while I was on ML) when I ran into him in the hallway, he said "you know how it is, you get an email on a Friday..." WTH and this is a guy I really like and respect.