What separates snapshots taken with a cellphone and artistic photographs is a real camera’s ability to capture many gradient levels of subtle detail. In graphic software such as Photoshop, Lightroom or Elements the addition of a controlled vignette further accentuate the main subject without showing up as a harsh “keyhole” effect so commonly seen when overdoes a vignette. When properly applied a vignette can draw the viewer’s gaze to the desired subject in the composition.
Personally, I use OnOne Software’s Perfect Photo Suite 9 to retain complete control of the vignettes I apply to almost all my photos. The idea is to not overdo it so that it doesn’t detract from the photo. Much the same can be said about any post processing editing.