Yeah another thing to keep in mind is that many people have two different size feet. Many people will just measure one foot and not the other one.

You have to size to the larger foot, which seems to me is generally the left foot. If it is only a half size difference you're probably okay with one pair of shoes. Although, I've seen people who have had to buy two pairs of the same shoe in different sizes (one in size 8, the other in 9.5).