Latest update to the StumbleUpon toolbar puts a "See Friend Reviews" link in the "applications and sign-in" section of Google:

http://mrbene.net/images/stumbleuponandgoogle.png

It's the same style as the rest of the links – I wonder how long that'll last.

Is that button on all sites, just in a different place?

If so, it could be a side effect of interactions between it's and Google's code to place it there.

If not, I don't think it should be there

I have been using stumbleupon quite a lot and they do have quite a lot of javascript injections into search engines, but I always click no, at the moment they ask you whether you want it.

David – The difference here is that the 3.15 update puts the "Opt In" button (the "See Friend Reviews" button) in the Google source, instead of prompting with a one-off JavaScript pop-up. In other words, they are now always asking if you want it, until you accept that you do want it.

It shows up in Reader, which is really annoying, since there's pretty much no way StumbleUpon could insert reviews into results (and if it tried, I'd be mad).

I just saw this tonight as well. StumbleUpon you are getting disabled from my plugins.

Looks like the version 3.16 provides a method to remove this functionality: "Adds an opt-out close box for the temporary links on search pages and Facebook."

http://www.stumbleupon.com/changelog.php

Still, a couple weeks without StumbleUpon, and I'm glad not to be using it anymore. I'm actually getting to sleep an hour earlier, and getting more done.