I've been creating user voted systems before there was a digg and they all have a fatal flaw. There are a extreme group of hardcore users that end up controlling the voting system. People think that digg is democratic but it is the furthest thing from it. As this blog post here shows, 66% of all stories posted on digg that make it to the homepage and pushed there by the same 60 people. Digg is essentially a community of 60 unpaid editors, and eventually the only new hardcore editors to join digg will be those with agendas and interests like the core group. This is because people with different interests will leave as they are pissed when their stories don't show up.
Now the netscape digg clone at beta.netscape.com has human editors to balance out the "user editors". This in theory should keep netscape grounded in the mainstream and stop cliques from forming that push agendas. The new digg clone is headed by Jason Calacanis at AOL and judging from the lack of rants on his blog the past few months they must be working hard to find ways of giving this thing some traction.