I really don’t think the Digg model is scalable for millions of users instead of the thousands it has now. Because of the simple fact that the more users you have the more submits you have. Making most of the better stories go unnoticed because it’s buried with all the mediocre submits that are found on the diggall page.
More users only creates more of a Slashdot scenario because the diggs that are on the homepage will inevitably be from more popular users like the tech tv crew, pacino and a few others. Because people eventually won’t/can’t shuffle through the mess that is already taking place in the diggall bin instead they will turn to the “trusted” submitters making those few the publishers of digg.com.
Solution (can’t bring up a problem without a solution now can you?), a digg extension for browsers so you can digg pages no matter where you are. Might sound absurd since I stated the problem with digg is too many submits and this “solution” most likely will result in a dramatic increase of Digg submits, eventually digging the entire web. But the author/publisher is gone and the ranking of pages truly begins creating an “attention trust” for search.
Ranking, something that Digg has is something that search needs desperately. If Yahoo or Google could capitalize this, buying digg in the process, it would revamp search to the point it needs to be.