Here's a great article (http://1-800-magic.blogspot.com/2008/06/back-to-microsoft.html) of Sergey Solyanik who left Google and is back to Microsoft.  His views are rather interesting and you can found some below.

So why did I leave?
There are many things about Google that are not great, and merit improvement. There are plenty of silly politics, underperformance, inefficiencies and ineffectiveness, and things that are plain stupid. I will not write about these things here because they are immaterial. I did not leave because of them. No company has achieved the status of the perfect workplace, and no one ever will.

On the other hand, in my year at Google, I could not figure out what was it they were doing. The better manager that I had collected feedback from my peers and gave it to me. There was no other (observable by me) impact on Google. The worse manager that I had did not do even that, so for me as a manager he was a complete no-op. I asked quite a few other engineers from senior to senior staff levels that had spent far more time at Google than I, and they didn't know either. I am not making this up!

On the other hand, I was using Google software - a lot of it - in the last year, and slick as it is, there's just too much of it that is regularly broken. It seems like every week 10% of all the features are broken in one or the other browser. And it's a different 10% every week - the old bugs are getting fixed, the new ones introduced. This across Blogger, Gmail, Google Docs, Maps, and more.