Just goes to show that SSD is probably the best upgrade you can make in any laptop. I wouldn't buy the Apple one though because there are better 3rd party SSDs (Intel in particular).
The Intel X25-Es are excellent indeed, have one of those in a server for the sql database. The new Crucial C300s are also insanely amazing. I think they might even top the Intels. Installed one in my old 17" macbook unibody, and couldn't be more wowed.
However, what happens when you need to use AppleCare and you have a third party drive installed? I've yet to find out, and I sort of don't want to.
The particular thing about the 512gb option this time around is this: You may have tons of options for 256gb and under drives, but you have nearly none for for the new 512gb drives Apple is offering. There's no X25 or C300 in 512gb yet, unfortunately. If you went with one of the few 3rd party options (the likeliest of which seems to be from Toshiba), it's likely *exactly* the same brand and type what Apple is using.
Furthermore, I've yet to really see 512gb drives I can order myself for under $1500, whereas the Apple drives comes to something like $1196 after the corp discount (and anyone can get such a discount, btw, just by joining something like photoshopuser.com).
In this -- admittedly rare -- case, getting the 512gb directly from Apple seems to make too much sense.
It's cheaper than going 3rd party, it's already installed (saving you time and/or installation fee$), it's likely the same model you'd buy for $300 more, you get the warranty from a single source, and no potential AppleCare conflicts. Quite a few pros, without any substantial con in site except the initial buy-in price itself.