Can't say yet.
I do think the $50 M didn't generate any noticeable sales - i.e. I think GTA IV sales on 360 would have been roughly what they were without the promise of the DLC, more importantly so far I don't think the promise of DLC has generated much in the way of additional console sales for 360.
However once the DLC is released it could generate a second wave of GTA IV purchases so we won't know until the DLC actually hits.
The real test will be whether we see more 360 console sales driven by the DLC when it releases.
I'm not holding my breath though and at the end of the day if I was a betting man (which I'm not!) I'd bet on the DLC not delivering what MS wanted for $50 M which was a big spike in 360 console sales driven by masses of gamers buying a 360 just to play it.
Try to be reasonable... its easier than you think...
