If someone is paying me to ship them something, I try to ship it immediately. I expect the same from others when I buy their stuff. Nothing worse than having to nag "did it ship yet? did it ship yet? did it ship yet?" constantly.
It's not that hard to get stuff shipped. Also I become vindictive if something doesn't ship, and I may end up tracking down your home phone number to see why I don't have stuff I paid for yet. This has actually led to two interesting stories. In one of them I ended up getting the guy's wife's cell phone number through Facebook. Another time I not only tracked down and called a kid's mom, but I froze his paypal account for a while because he was jerking me around.