The Nourishing Traditions cookbook has a big emphasis on the importance of soaking grains, beans, seeds, and nuts in an acid medium before they are cooked, turned into bread, or eaten raw. The reason this is done is to disolve phytic acid to enable our bodies to properly digest these foods.
Phytic acid, or phytate, is found in most grains, beans, nuts and seeds. It inhibits the body from absorbing certain nutrients, particularly minerals and iron. Soaking really helps to break this acid down in most grains, beans, nuts and seeds, but it's not as effective for some of these things as it is for others.
I personally believe it is better to eat oatmeal that has not been soaked, than some sugary boxed breakfast cereal, or unsoaked nuts as a snack rather than chips. I soak some things and I am experimenting with more recipes. I always feel really good about myself when I soak these things and like I'm being SUPER healthy :-). From what I've read, it seems that those with greater health needs should pay more attention to soaking, but if you are in good health, it's not as big of a deal.
Here are several good articles that gives more information on phytic acid and how much difference soaking makes.
Phytic Acid: Tips for Consumers from Food Science
Oatmeal and Phytic Acid
Phytic Acid: Defining and Dealing with a Common Antinutrient
Here's a short video by a woman who has done a lot of research on the topic.