Well the market seems to be settling and the difference looks like it will be back to its 30-40K a week fairly soon.
I'm willing to guess at an average of 40 K per week over the year advantage for PS3
This would translate to a catchup per year of 2 million units so it will take PS3 nearly three years to surpass the 360.
This of course assumes all things remain the same. This we know will change with the release of Natal and Sony Wand.
Also in 3 years I really doubt this gen will still be current as at least one of the nex gen consoles will be here by 2013.
The new gen machines usually launch at 6 year intervals so early 2012 is my guess.