PRS-505 here. You don't find the 5" screen too small? For books with proper zoom text re-formatting, not an issue at all. But otherwise, I find myself complaining even with the larger screen.
The zoom on the 300's really good for epub, not so hot for PDF. I tend to find with PDFs that it's hit and miss as to the formatting, but PDFs that are effectively scanned images are pretty much off because of the size.
I find the screen size (roughly the size of a paperback) is fine for Epubs though, which is what I mainly use for tech books. I also like the fact that it fits in the pockets for my shorts. This summer I went to an Island in the mediterranean and went through about 10 books in 4 days on the thing. Carrying the 10 books would've meant less room for luggage. Being able to take 200-odd books to the beach is pretty awesome.
I find the screen size (roughly the size of a paperback) is fine for Epubs though, which is what I mainly use for tech books. I also like the fact that it fits in the pockets for my shorts. This summer I went to an Island in the mediterranean and went through about 10 books in 4 days on the thing. Carrying the 10 books would've meant less room for luggage. Being able to take 200-odd books to the beach is pretty awesome.