WT Sharpe - Oh, I agree, larger screens are better for PDFs, and the 7-inch aspect ration doesn't lend itself well to them. However, bigger isn't always better for some users. My fiance has an iPad2 at work and he thinks it's too big. He just doesn't use it, but he likes the 7-inch size. Of course, he does a lot of email and browsing with his smartphone, so zooming in to stuff doesn't bother him at all.
But to prove everyone's got their own taste: One of my classmates uses his Kindle Keyboard in class for PDFs. Has it in landscape, doesn't bring a computer (this class is mostly discussion, since we do all the work online), and just smiles as we all look for plug-ins for the laptops (long class).
If I was getting a tablet for work/school stuff, I'd prefer the 10-inchers. But I don't like reading or watching stuff on the Galaxy that much; enjoy it more with the 7-incher.
I think the 8-inch ones would be a nice compromise. I looked at the Vizio 8, but I wanted more than 2GB internal storage (that's what's left to users, and you can't shove apps onto the SD card).