Combine reddit.com and blogger.com to get a site where you can create forum/social bookmark sites about any topic you want in two minutes.
reddit.com is a good site. A bit of a forum site, a bit of a social network site. Unfortunately it has grown in size the as it has grown the content that is found on reddit is more general and there is a lot of group think. Overnight there are dozens of articles about impeaching the president or electing Ron Paul or some random big news story of the week. The more users that sign onto redit the more general the topics become. Breaking news is much more likely to survive then a link to a published science paper no matter how good it is. About a year ago reddit started getting kitten pictures and today many programming articles don't make it to the front page anymore.
With tags and filters one would be able to ignore the latest reddit fad, but there is something that tags could never fix. If you submit an article about an interview with a comic artist there is probably more people on reddit who will mod it down then up. Now if you were to go to a comic forum/social site that same article might be the top article and debated in depth. Topics that are not in the mainstream, but nitch don't work too well on social bookmarking sites like reddit. Many people have taken the approach of created there own reddit/digg clone specifically for a nitch. http://truemors.com/ lets you submit rumors and http://www.huffingtonpost.com/ lets users vote on pre-identified blogs (including themselves) are just two such clones and there are many more. Some of these sites have been coded from the ground up, but there is starting to be programs you can download and in install to get a digg clone. This is just the next generation of the bulletin boards from ten years ago. You still have to own the domain, hosting and perform all the maintenance on the site.
blogger.com provides a nice service, before blogger.com typically you really had to setup your own domain and have your own blog, but after that in five minutes flat you could have a blog. Heck you could have ten blogs about ten topics if you wanted just as easy. Now if you were to have a site like blogger.com, but rather then making blogs, it would let you create reddit clones. Create a social bookmark site around any nitch you want. If there is a community then it survives and if not, well it was only a few minutes of work to set up.
Slashdot, K5, digg, reddit, one by one they have risen and then what was once so nice, fills up with junk. The community moves on to a new social site. Well they don't move overnight, first someone has to make a new site for them to move to. With this social site overnight a new community could be created. A community can fracture in a nice way. When Ron Paul became big anyone could have overnight made a Ron Paul social bookmarking site where every single link could be posted and appreciated rather then the slow death on reddit where eventually everyone was voting down Ron Paul articles, not because they were bad, but simply because they were about Ron Paul.
The idea that reddit brings is good, good enough to be bought, but bigger then them would be a site that lets you make sites, thats a site that Google would buy.
Update: I have informed of one such site that is trying to do just this (and looks quite reddity): dailyhub.com
Update: And another site http://slinkset.com/ and a site that just for comments: http://disqus.com/