i probably won't buy it if it only has 512 mb. on the ipad 1 i got constant crashes with pdfs because it lacked ram. the ipad 2 largely solved this problem, but page renders are slow, and i still get crashes. my aim with this upgrade is to take advantage of the beautiful retina display AND be able to read my pdfs better. no crashes on the asus transformer (1 gb ram), so apple needs to step up their game.
i am sure less ram is fine for most use-cases, but for reading large pdfs (for some reason, ones with un-optimized color images in particular), it is a real pain. even my netbook from a few years ago has 1gb ram...
it wouldn't be stupid of apple to be stingy with ram, and some users might not even notice, but i would 🙁