I anticipate around 10 million sales per year on average, until the release of a "PSThree", then I expect the PS3 to sell around 15 million on average.
So 2007 + 2008, about 20 million, I anticipate a slimline PS3 to launch somewhere in 2009. By the end of 2012 about 80 million sales. I do expect the PS3 to stay commercially available for much longer though, so by the end of 2016 about 140 million (triple the amount of 360s I anticipate for the long run).
Of course there are endless yet unknown factors. But I certainly expect the PS3 to go well beyond 100 million for the long run.