Y-Y-Fb-Ms-Dg-Yt
From the Compete blog:

There is certainly something magical about reaching 20 million. Web 2.0 darlings, also prime acquisition targets – Digg and Facebook both crossed this milestone last month.

* Digg edged out Facebook, with 2.3 million additional unique visitors
* Facebook is growing 3x faster than MySpace (on a percentage basis)

For what it's worth, Quantcast says Digg has 6.9mm in the US...