I think there will be an initial flood of clones, but only maybe 3 or 4 semi-successful ones. Remember how everyone said there would be a billion Slashdots when Slashcode was open sourced?

I concur. Several years ago I wrote a "clone" of MetaFilter (which was quite popular at the time) called FreeFilter. A bunch of *Filter sites sprung up with only a few actually "sticking." I don't believe any continue to exist now though.

Yes, but reddit looks a lot cleaner than slashcode.

I actually see this as a good thing for once. The internet needs more content/quality aggregators that are user-driven, not SEO/link-farm tainted. And niche markets are probably the best way to achieve that.

I actually hope this will be disruptive, and popular sites return to servicing their audience directly instead of relying on Digg, for example. Digg has become so popular that it almost needs it's own nested-digg now, a rather ironic self-defeating problem with social popularity and vertical growth. I mean, don't get me wrong... I suspect Digg will continue forward and be hugely successful.

Hats off to the reddit team.

I imagine getting critical mass is the hardest problem.

And the impending jump of the shark thereafter.