Gotta agree with LaCamera. I just spent an hour fiddling around with the "new" versions of my already-purchased books from the new Reader Store. I don't care for 1) the font, 2) the text being stretched nearly as far as possible to the edge of the screen, and 3) the left-only text justification. I had previously customized my font and it was quite readable. Now I don't think I have that option (yet), let alone any of these other display horrors with Sony's ePUB.
Also, unless I've done something wrong, the font size does not change with the font button on my Reader (a PRS-505), it just makes some kind of page adjustment. I'll have to investigate further. But I'll be keeping the old Sony format on the books I've already purchased and not buy anything else from the Sony Reader Store until I see an improvement or something althogether better. Ick.