The Hot page is the default page when you connect to Reddit, and with good reason, because it shows all the best recent stories.
But sometimes the content of the Hot page doesn't change very often. If you are bored looking at the same content that you just saw an hour ago, you can go onto the second and later sub-pages of the Hot page, to look for newer items, but this is not an efficient way of discovering new items, because those pages contain both newer items coming up and older items going down.
You can also visit the New page. Here the material is fresh and constantly changing, but it hasn't been filtered at all.
It would be nice, when you had read the Hot page, and you were still looking for new filtered material, if you could look at something in between Hot and New. For example, 50% Hot/50% New.
It's important to point out that when I say "50% Hot/50% New", I do not mean a mixture of the contents of the Hot and New pages, because that would just be the same content. What I mean is a 50/50 mixture of the criteria used to rank items for appearance on the pages. On a 50/50 page, you would expect to see items not yet Hot enough to reach the Hot page, but no longer New enough to remain on the New page.
Indeed, given that there are reasons why sometimes you want to read Hot, and sometimes you want to read New, there is a case for being able to read any combination of Hot and New, for example 70% Hot/30% New, or 20% Hot/80% New. It should be easy enough to provide access to these options with an appropriate URL scheme, like http://reddit.com/hot=70&new=30.
You might object that what I have described so far is entirely for the benefit of "lurkers", who just read the good articles, and never make the effort to read through unfiltered new articles and vote for the good ones (and vote against the bad ones).
Before we can understand the benefits of mixed Hot/New for Reddit readers who actually vote on articles, we need to consider the effect of a reader's votes for stories on the Hot or on the New page. For the purposes of this analysis, I will assume (optimistically) that each reader has only one Reddit account, and can only ever vote once for a story.
The problem with voting for a story on the Hot page is that it is too late. The story has already appeared on the Hot page, it has already been seen by a lot of people, and the most you can do is slightly alter how many more people will see it in the future.
The problem with voting for a story on the New page is that your vote is just one vote. It is very unlikely that your one vote will have any major effect on whether or not any other Reddit reader sees the story. Other readers of the New page will see it whether or not you vote for it, and it is very unlikely that one vote will determine whether or not the story makes it to the Hot page.
If we assume that in the future Reddit implements mixed Hot/New pages, and that different readers of this future version of Reddit read mixed Hot/New pages with different mixture levels, according to taste, then for every reader of a page with a certain percentage of Hot and New, there will be other readers reading a page with just a slightly higher percentage of Hot and a slightly lower percentage of New. For example, if you are a reader who normally reads the 30% Hot/70% New page, there will be other readers reading the 35% Hot/65% New page.
So if you vote for a story which is on the 30% Hot/70% New page, there is a good chance that your one vote will cause the story to be seen by readers of the 35% Hot/65% New page who would not otherwise have seen it.
The benefit of the "multi-level" Hot/New system is that voters at each level have a chance to alter what is read by voters at the next level. This creates more incentive for voters to vote, which in turn should increase the quality and quantity of stories appearing on the site.
In a two-level voting system, most of the work is done by users who vote on stories in the bottom level (which is usually completely unfiltered), and most of the benefit is received by all the users who only look at the top level. Providing multiple levels has the effect of spreading the workload around a bit more.
I remember not long ago when people used to compare Digg to Slashdot, but now it's always Digg versus Reddit. If some commentary can be made on the operation of Reddit, an obvious follow-on is to ask if the same commentary applies to Digg.
So, how would mixed Hot/New apply to Digg?
Digg's equivalent to "Hot" is the front page, and its equivalent to "New" is the "Digg for Stories" page. On Digg the promotion from New to Hot is a very discrete operation, since a new story "pops" out on to the very top of the front page when and only when it passes some threshold of combined hotness/newness while sitting in the Digg-for-stories page, or else, if it hasn't passed the threshold by 24 hours, it falls off the bottom of the Digg-for-Stories page. The "live or die" nature of Digg's treatment of submitted stories makes it less practical to incorporate a more gradualist approach to identifying success or failure.
However, it is already possible to alter the sorting criterion for stories on the Digg-for-Stories page, for example to select stories in order of number of votes. If this option was extended to allow sorting by criteria which involved both newness and the number of votes, and new stories were allowed to live on the Digg-for-stories page longer than 24 hours (or even forever), then the Digg-for-stories page could function as the equivalent of Reddit's New and Hot pages (and any mixture thereof), and a separate front page would be less necessary.
It is already evident that the distinct voting mechanisms of Digg and Reddit cause the Internet reading public to become exposed to different types of story.
It follows that there is probably other good material out there which we aren't getting to see at all, because the voting mechanism optimised for the discovery of that material hasn't been implemented yet.
Maybe we need not just 2 social websites, or 20 social websites. Maybe we need 2,000,000,000 social websites. Maybe the perfect voting system will only exist when each user has their own peronal optimised "front page", which is compiled according to that user's choice of scoring algorithm (where the score for each story is calculated as a function of the story's newness, the number of positive votes it has received from other users, the number of negative votes it has received from other users, and any other information deemed relevant).