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)
Yes. Several other programs try to do the same thing. I think Macromedia Flash player may be one of them. I know I have had to uncheck the Yahoo box three or four times recently. Obviously Yahoo has bribed a lot of other people to install load up their search bar alongside their programs.