The implication is that he'll be able to buy a boat. That's pretty much it.
Noah's Ark?
Flug has a point. Satoshi's sandwich acquisition in itself could cause a mass panic. If you are looking at the extremes, having that much coin doesn't help in smoothing out bumps unless you sell some upfront, and I'm sure many are watching for the early blocks like hawks, even if they are in smaller lumps (like 65k or something, which is still major, already). On the other end of the spectrum, Satoshi, whoever he/she may be, does not need to be evil. He could bequeath his wealth to an heir and a few generations later there could be a dynasty of dictators. Or he could be, and the dynasty is planned. Maybe 'Satoshi' is a team of NYC bankers doing the same as they did in 1910, a carefully planned execution of cornering the market before it even exists. We simply don't know.
Then again, supposing Satoshi is a benevolent saint, there is nothing preventing the current elite from simply starting to use Bitcoin too and reestablishing their hegemony. I don't mean buying up real estate on the cheap (or at expense later). Rather, a certain kind of person will do the same kind of thing whatever tools he has at his disposal, and be equally successful at it, because the rest will let them, just as it is now. A turd always floats to the top, regardless. Bitcoin's given technical properties cannot change human nature.
Anyway, it's far more likely no mainstream merchants will ever adopt Bitcoin because of pressure from the established banking system, supported by the occasional FBI raid on anyone falling out of line, starting with the exchanges, perhaps supported by some technical attacks on e.g. the bootstrap IRC channels. I don't believe they will need anything like a 51% attack, but if so, pretty sure some agency can be tasked with putting together the appropriate ASIC farm.