My Dd3 is just about to turn 6 months and I'm quite shocked by how mobile she is!
She began to crawl at about 4 1/2 months (using her knees to push herself forwards), and now perfected she can move at quite a fast pace. At 6 months she is now pulling herself up to stand on anything she can find, and is even trying to let go and balance on her own! 
My first child was pretty much average in this department. My second was walking by about 9 months or so.
Just wondering how many others have experienced this?