This is something that I would have written about eventually, but he covered it just recently, and very well.
http://waiterextraordinaire.blogspot.com/2009/05/three-reasons-why-i-always-repeat-order.html
The link says it all.
He also talks about the importance of writing everything down. I’d add that, while the server might think that it makes them appear to be super competent and amazing not to write down an order, the guest is only impressed by getting their food correctly. Maybe you have perfect photographic recall and don’t need to write anything down. You still need to write everything down. Really. If you want to do parlor tricks for your guest, learn how to make balloon animals.
Also, it’s amazing how much of the noise of a restaurant tends to settle like a smoke cloud right about waiter eye level. Since your ears are right by your eyes, it can sometimes make it hard to hear the difference between medium rare and medium well, especially if someone is deep in a booth. I know that I’m sometimes corrected when I repeat the temperature back.
Finally, believe it or not, mass delusion can sometimes set in. I remember one time, I repeated back the order and I wrote it down exactly as it was repeated back to me. When they got their food, they claimed it wasn’t what they ordered. The person next to them chimed in, “I heard her and that’s not what she ordered”. So, there are times when repeating the order back won’t help cover your ass.
Still…repeat the orders back.
That’s an order.
So You Want to Be A Waiter
So You Want To Be A Waiter 
Thank you for mentioning the post. It is always good to write it down.