Share buttons and the social network icons for digg, twitter, facebook, etc. come in all shapes and sizes. When speaking to middle-america though, it is safe to say that most people have no idea what digg or StumbleUpon are.
Is there any usability research about styles for this section of your blog that are effective in driving engagement? What designs have you seen that look really good and effectively communicate "share"? I'd argue that the tried and true, "email this" or "invite" might be more familiar to most non-internet savvy people such that sure, while we WANT people to digg and twitter us, at the end of the day we really just want more readers and more of our readers spreading the word.