Using a KW-anchor seems to signal "higher spam probability" in the eyes of Google.
They often stress for example they don't like articles and press releases with WW-anchors. Some links are o.k. with an URL anchor, but a KW anchor seems to prick up Matt Cutts ears.
For example a signatur link in a forum where I sometimes post or a link on the "recommended links" page of a friend who has the same job. Does an anchor raise the chance of being unnatural in the eyes of Google?