I try very hard not to compare Caroline's milestones to Emily's. But I distinctly remember that by Easter of 2011 (when Emily was about 9 months old) she was crawling and while we were visiting my mom that weekend, she pulled up. Very soon after she was cruising around furniture.
Caroline, however, has been content to lounge around like a potato -- with no signs of getting off her butt to move around, and actually getting mad when she found herself on her stomach and no one was there to immediately sit her up again. BUT last weekend (in the midst of having pink eye and yet another double ear infection) she found time to learn how to put herself into a sitting position from hands and knees. Next was pulling up on the side of the crib.
So we immediately lowered the crib (not that Caroline would bother exerting the effort to throw her leg up over the side of the crib and try to get out... but I did worry about her leaning too far forward and falling out head first).
She's also taken to sleeping on her tummy -- or on her knees.
She's been crawling now for a whole week and a half, so this video is a bit outdated already, but...