Any value to delicious, Digg, etc. buttons?

Has anyone documented whether people use them?

[anax]

I'm seeing an increasing number of sites (especially newspapers) with a row of buttons on each page to "Add to delicious", "Add to Digg", etc. [Insert your favorite social or bookmarking site here.]

Yes, I know having one person bookmark a page is worthwhile. But is there any evidence that these buttons result in anything more than the rarest additional linking? I ask because I thought most people who use sites like delicious have installed browser widgets that let them bookmark automatically, with no need for the on-page button.

[rogerd]

That's an excellent question. I've added social bookmarking links to a few of my blogs, but I can't say that I've seen any increase in traffic from any of those locations. The most effective one seems to be stumbleupon, which produces modest bursts of traffic but little incremental revenue. Most stumbleupon users probably click their toolbar, though.