The "click to upvote story" patent would be extremely valuable if someone ever found themselves in a patent dispute with Facebook. I can already see a lawyer explaining to jurors how a 'like' is the same as a zero length 'digg'.
Don't want to get in to whether the system should or shouldn't work this way, just that given the way the current system does work that the patent could easily be worth $4 million.
How is this feature any different from the old Everything2 engine which dates from the 1999-2000 timeframe? The PerlMonks system, built with the same engine around the same time, also had a "one click vote" on answers not unlike Stack Overflow only a whole lot uglier.
Facebook's "Like" is surprisingly new; I found a Mashable article[0] from the day it was released in April 2010. Digg, on the other hand, is surprisingly old[1].
Don't want to get in to whether the system should or shouldn't work this way, just that given the way the current system does work that the patent could easily be worth $4 million.