Today while I was talking with a couple of developers from Bioware, I asked about digital distribution on the PC.  They told me that they recently secured a deal with Steam for Mass Effect 2.  A quick search in the Steam Store reveals that Mass Effect 2 will be available on Steam in time for the January 26 release date.  The only thing missing is a price and whether or not a preload will be available for the next installment of the sci-fi saga.