A WebmasterWorld thread claims a Google AdWords representative sent him an email warning him not to use the add to Google Reader RSS button on his site. Why did Google tell this person to not have the button on his site? Well, because the Google Reader button has the Google logo within it, and you need Google's permission to use Google's trademarks prior to posting them.
Here are the exact words of the email, I believe;
It has come to our attention that your website is using Google's trademarks without our permission. We allow use of our logo only if we have granted express written permission to do so. Please remove the Google logo from your website until such time as you obtain permission and approval for its use.
Um, check out the Google Reader Blog, do you see the button they use on the right side?
What about Google's Help People Subscribe to Your Content page which has the button there for this specific use.
Obviously, this is a gross example of Google's representatives not being educated in Google's other properties.
Forum discussion at WebmasterWorld.