You know that annoying kid who is constantly poking you on your back and asking the same annoying request over and over again? Well, Google said if you do that to them, at least via the Fetch as Google feature within Webmaster Tools, it won't lead to a penalty.
A Google Webmaster Help thread has one webmaster concerned that if he uses the fetch as Google feature too often, it might annoy GoogleBot too much and lead to Google ignoring his site completely.
Google's John Muller said in response, "there's no penalty for using "Fetch as Google" frequently."
The original question was posed as:
I am wondering if their is a penalty for using "Fetch as Google" too frequently. I have been using it a bunch, trying to tweak a page on my site to get it ranked better. At first it was very useful. Then, all of a sudden, it seemed like the more I used it the worse I was ranked. Can using this tool too much really hurt you?
John said no, but bad links and bad content can.
Forum discussion at Google Webmaster Help.