I'm looking at CloudPull to back up my Google data. Yes, you should back up Google data. No, I don't think my local hard drive is more reliable than a Google data center, but hardware failure is the least of my concerns. Consider what would happen if you lost access to your Google account. Um hmmm... Now see how many ways you can think of which would cause that to happen. Still think you don't need a backup?
Oh, and when I search my files on my Mac, I expect to find all of my files -- not all of my files except my Google Docs.