I have a hard time putting the baby down, too, and mine is almost 6 months old! One of the good things about having six older kids is that there's almost always someone available to hold the baby :-). Of course, he didn't roll over until last week, because he's never on the floor long enough ...
It is so hard to put her down! We have tummy time every day for a bit, where we play on her play mat. She likes the mirror, is very alert and looks around, but my favorite time with her is either when she is nursing or when she is asleep on my chest after nursing. I can't wait to watch her grow into a 6-month old!
We should all post pics of our kids to share, I love kid pics!