falsepositive - 4:45 pm on Jan 6, 2012 (gmt 0)
To prevent such new sites from ranking, G needs to readjust their domain age filter further and put more weight on links. The way it's going, they can easily just change their balance any which way at any time so eventually, the new/small site strategy may not last long either. With each Panda run, you'll see a new purge. I'm guessing that what you are seeing with new sites ranking is the "honeymoon" period, perhaps to assess their worth (in their current standing). Then they are subsequently demoted after that period. Also, perhaps those sites have not been hit by a Panda run as of yet?
Is it possible that at some point, the algo quality cycles will happen much more frequently so that the clean ups happen in real time -- if so, then spam of this sort may not have long to exist. My observation is that there doesn't seem to be any permanence to the SERPs anymore.