In the last two weeks, Mac's development has advanced so much. In addition to crawling, he can get in and out of sitting and pull to stand (not from the floor quite yet but from a stool). He is taking steps to the side and forward with help. I guess he is planning on putting on a show at his birthday party this weekend!
After this video was taken (please note he crawled for daddy!), he pretty much refused to do it again. We tried until he went to bed. But then this today, after having a slow start, he just took off. It still isn't "easy" for him and he has to work at it, but I honestly can say I feel like he is a crawler (not just is able to crawl). And I already miss the days when I could put him down and know where he'd be moments later. I have to change my bad habits for sure!