Well worth the $2.99 I payed for it. Its pretty much an electronic version of the book, but with sounds and much faster searching. The added features are what makes this app so nice, particularly the ability to make different lists, like "life birds" and "yard birds", then add birds to them. You can also click on a bird you identify and add an "event", which will record the bird, the time, the date, and the location, all automatically. Theres a lot of birding information, as well as a quiz section too.
Only negative: it crashes quite a bit, but not enough to impact me too much.
jjnowak1980 about National Geographic Birds: Field Guide to North America, v3.5