Thanks for the responses! After looking at the dove picture, I think I’m seeing part of my problem outside of macro shots: I’m not giving enough distance from the subject to the background I want to blur out. 🙂 The “prime” explanation has been the best I’ve heard so far, and it makes perfect sense. The 50mm lens gets mentioned a lot in books and forums, so I think I’ll start looking there.
And thanks for the information on the other lens manufacturers. I know the Nikon stuff tends to be on the pricey side; it’s nice to have options!