I was actually going to try oak on another bow, too. According to the Bowyer's Bible, all sorts of white woods (like hickory, maple, and oak) will work. From what those bowyers say, hickory is the best of the white woods. I am really looking forward to getting my hands on some Osage (but not until I get more skills).
And I have thought about using the store bought wood, but I am still not totally confident I would be able to choose a good board. Like you said, it is not a simple task!
If you're looking at an oak board for a bow, you really have to examine the end grain and the way the grain follows the length of the wood. Finding a board where the ring travels the length of the board is difficult.
Another wood that I would like to try for a bow is ash, it's supposed to be pretty strong and flexible.