Yup, good info coming from this thread - to help explain visually, I just took these two consecutive shots in the garden. They are hot off the camera and never even had a whiff of photoshop... resized in iPhoto, but orig files are linked to.
Nikon D300 w/ Sigma APO 70-200 f2.8 Macro with both photos taken at 145mm
With the aperture as closed as possible @ f22: Note at this aperture in the morning, the shutter speed is quite slow (1/10) so there is motion blur on the flower.
Original file
Now, with the aperture fully open @ f2.8 (1/640 sec), the way a blurry background makes the flower stand out is great! Even the flower's leaves which are right next to the flower.
Original file