The drive will be sold as a standalone product in Japan starting March 11 for roughly $170, according to this Impress press release. Stateside, Microsoft currently sells a 120 GB hard drive for $150.
Microsoft could bring the 250 GB drive to western markets soon, but not necessarily as a standalone product. Last month, Kotaku reported that the Xbox 360 Elite, which includes a 120 GB drive, was out of stock at Best Buy, Wal-Mart and Gamestop. This suggests that Microsoft is clearing out inventory to make room for Xbox 360s with bigger drives.
I could see why Microsoft would want to pack 250 GB hard drives into its consoles. The basic Playstation 3 slim includes a 120 GB drive, so Microsoft would have one more selling point for the Xbox 360. A standalone drive could theoretically follow, just to even things out.
But to the original point, a 250 GB HDD isn’t necessary, especially if you’ve already got a 120 GB drive. So much of the Xbox 360 is streaming, including 1080p videos in the Zune Marketplace, Netflix Instant Watch movies, Last.fm music and your PC’s entire music and video library. I’ll admit that my Xbox 360′s 20 GB drive feels cramped (though I still have about 5 GB left), but latecomers who got a 60 GB or 120 GB drive won’t have that problem.
Extra storage is best-suited for people who install lots of games to the hard drive and never uninstall them, download insane amounts of Xbox Live Arcade or On Demand games and prefer to put all their music and movies directly on the console. If all three scenarios don’t apply, I imagine 120 GB will be enough, especially given the price of Xbox 360 hard drives as a whole.