As one of the best titles available on the PS3, the game will continue to sell through the holidays.
By next holiday season, possibly earlier, it will become a greatest hits title, which will make it an easy choice initial pick up title for new PS3 owners.
It sold over 1m on Day 1, and its performance has been on par with previous MGS games so far. Didn't add up the numbers, but it looks like it's been edging out MGS3 in sales which would make greater overall sales a logical conclusion.
Considering the vast difference in user bases between the PS2 and the PS3, that amounts to a better attach rate than any previous MGS game, which is likely to be reflected as the PS3 user base expands, particularly as a greatest hits title.