I use an "add this" button (google it) because of the clutter of having individual buttons. It lets you add to whatever social network you use. I haven't been digged, but I think I'm going to start digging my own posts (I know it sounds sad) because I get hits when I stumble my posts (I swear I'm not as pathetic as that makes me seem). If the next digger/stumbler likes it, they can do the same and you'll get lots of hits (I wrote a post about GenderAnalyzer for blogs that got a much higher number of hits through stumble than average because other people continued to stumble it) and so you've started the cycle for yourself :)
I think it's technically against Stumble Upon's rules to stumble your own posts...although I admit that I do it. Would anyone be interested in forming an informal group where we stumble each other's posts?
I didn't know that Stumbleon didn't want you to stumble your own things--I mean honestly what harm can that do--but I say we just try to make a concerted effort to stumble each other's posts when they're good. That's the point of Stumbling anyway, to share good stuff. :)
Meg--I didn't realize it either until the guy who writes an internet marketing blog that I read said that he was banned from Stumble Upon for stumbling his own posts. He argued the same thing that you did--that the whole point of SU is to make interesting content easily discoverable by other people interested in that topic--but I guess the folks at SU think that stumbling your own stuff invites abuse? Who knows...