It seems to me that the point of Digg -- and by extension, any of the different social network aggregators -- is to provide a mechanism for a community to discover things that are of interest to other members of said community. Someone submits something, and other users who agree that it is cool go ahead and "digg" it, increasing its profile in the network, thus drawing in more eyes. This creates a layer of trust among the community; if a bunch of people dig stuff, chances are you might like it too. People involved in said community know the sorts of things they want to digg, and have mechanisms allowing them to easily do so when they come across something they want to share. This may be browser extensions or bookmarklets or what-have-you, but I maintain that active Diggers don't need a little button on every one of your posts to digg you.
So therefore, the only purpose of including said buttons is to incite people -- people who otherwise wouldn't be bothered -- to go ahead and digg you. I mean, it's just one click right? What does this accomplish? Well, in the short-run it might get a few more eyes to see your content, but in the long-run what it accomplishes is a dilution of the network. If suddenly a bunch of people start digging your content because it's easy rather than because it merits digging, pretty soon the whole system is going to break down. Who wants to use a social network where everything anyone ever creates gets submitted? Not me.
(But in full disclosure, I don't use any of those social networks now. I just see the value they currently hold, and understand that this value will very quickly dissolve with sudden influxes of uninteresting content.)
Sure, everything is of interest to someone -- the fact that a handful of people see my content attests to this -- but I can't imagine submitting any of it "to the masses." If you're creating something that you think is diggworthy, then by all means throw a link in and beg people to digg it, but automatically doing that on everything you create is just plain arrogant. Chances are, many people who might otherwise digg you will not do so because it seems as if you're begging for it. I submit that by putting said links in, you are begging for it.
My first shorter rant on this subject incited Matthew from eJabs.com to comment that he thinks I may have a point, and that he may consider getting rid of his automatic digg links. The fact that he took time out to tell me what he thinks and that he may change his site as a result of it suggests to me that it'd be OK to use his site as an example. Take a look at this:
That's what's at the bottom of every single one of his posts. Clicking on any one of those little icons will submit the current post to a different social network aggregator site. This may seem like a pretty extreme example of this type of pandering, but I see it pretty frequently. I bet you do too. I was going to link to a handful of them, but decided to just use the one person I've heard from as an example. (Matt, I like your site and am not picking on you!)
So I guess what I want to ask is: when you view content and see links like that, do you click them? Why would you expect that anyone else would either?