I am very satisfied with my Sony DPTS1.
Was lucky enough to snag it in the last sale from BHP in late July
DPTS1 is amazingly light for a 13 inch device.
UI is also nice, does not get in the way.
So far it has handled all PDFs with ease.
There is an expansion slot for microSD cards up to 32GB size.
Minuses are the obvious, no epub support despite the built in web browser so it should not have been terribly hard to add support. I have other ereaders for epubs, but much prefer reading on DPTS1.
No frontlight, but not an issue if you read in normally lighted areas.
Another small con is no physical page turn buttons.
Positive is that there are well designed physical Back, Home, Options, Power buttons.
DPTS1 comes with a black fabric sleeve which is convenient enough for storage/travel.
The note taking with the pen is pretty nifty too, I could see how it could very useful for study. You simply write over the pdf and it gets saved (with a new layer I suppose)