This is a big win for Digg. Over the last six months, I have seen a significant increase in the usage of Digg by college students, and this inclusion in the Facebook Mini-Feed will only improve its reach in that demographic.
A concern that I have with the integration is that your Mini-Feed will probably become really cluttered with Digg stories, if you are a heavy digger. Digg does, however, have a Facebook application that keeps your "dugg" stories neatly in a module on your profile page.
At this point, I haven't decided whether I like the application or the Mini-Feed approach more, but I do think that it is great that Facebook is integrating these third-party sites and turning users on to more Web 2.0 services.