Yahoo toolbar is constantly trying to sneak itself onto my computer. If you download other programs, you often have a box checked by default saying that you also want to install the Yahoo toolbar. It's a real pain, because it can easily get in under the radar screen.
I haven't seen Google do anything like that.
The Adobe Acrobat update tries to force the Yahoo Bar thing, just move it to the left or unclick it. (sorry I don't remember how I got it off the install screen, but it can be done)