Today, I can across this article while looking at my iPhoneFlow updates on Twitter.  Essentially, they show you how to set custom colors in the table cells of a table view.  While using a standard table view is relatively easy, trying to set properties for the grouped table view (the one with the rounded corners) is not as easy.  This article does a good job of showing a workaround if you want to customize the background color of your table cells:

http://pessoal.org/blog/2009/02/25/customizing-the-background-border-colors-of-a-uitableview/