I have noticed looking at the EXIF data that the F stop that gives me the a blurred background that I like and makes my subject stand out on my zoom lens without totally making the background unrecognizable is F 5/6. This gives me a nice blur without going too far. I haven't tried my new F2.8 70-200VR but I do like the effect of my previous pictures with the 5.6 setting.
So what is your favorite F stop in situations like this? I guess I am wondering just how much of a blur you like, Jeff
Example of mine below at f 5.6