I got online at work today in the attempt to track down what the problem with my machine was, and the first link I clicked on gave me that answer, I think. The first link I went to said that iStat Pro (A widget that tells you about the resources of your machine) did not play well with Macbook Pros and would cause them to not go to sleep when they are shut and not wake up properly when they are opened.
I removed the widget and haven't had a problem yet, but it is still a young fix. I am not confident until I get a couple of days without the same problem.