The most important thing users should remember :

If you have a LOT of friends (50-100 or more) you will need 2X or 3X as many diggs as a new user, to reach the frontpage. This is proven and 2 of the top10 users confirmed it to me. It’s natural that Digg implemented this for powerful users, because their friends dug their articles, so they have an advantadge over a usual starting user with just a few or NO friends. So if you are a very new user with no friends, you can get to the frontpage with 25-35 diggs.

Algorithm changes like this are the reason I stopped being an editor on Shoutwire (a digg clone)

It got to the point where anything I submitted would get buried to the 3rd page before it got the required "shouts" to make it to the front page. So they hand picked me to write editorials, then buried them before anybody could see them.

I ultimately see sites like these failing really soon. What's the incentive for a user to submit a site or "digg" a site other than their own?

There is none... and that's a problem.

> What's the incentive for a user to submit a site or
> "digg" a site other than their own?

I think this boils down to the question "why act selfless in a society?" and probably contains similar answers, too... certainly a broad topic, but there can be many reasons why people act altruistic...