I have invested in an IREX Digital Reader DR1000. The sum total of its features and shortcomings appear to be ill defined, somewhat the sum of a conditionally convergent series. So I really have developed a love-hate relationship with the damn thing. Let me get the negatives out of the way first:
It's way too expensive. In fact, I wouldn't have bought it if it weren't for the fact I am on sabbatical and need easy access to piles of papers without the paper.
The battery life is too short, definitely shorter than advertised. A couple hours is no problem, so it's good for note taking in lectures. However, it couldn't keep up with a full day at a conference. Also the battery is not user replacable.
It's too easy to ruin the charging connector if you try to use it while charging. In fact the whole device is a bit too fragile.
The software is buggy and crash prone (but not horribly so). There have been software updates, but they are too rare and don't fix enough bugs. Also it takes a couple minutes to boot, which is bad if the device crashes while you're taking notes in a seminar or meeting.
The digitizer is a bit off, enough so that drawing nice pictures is impossible. (Rough sketches work okay though.) It's especially bad near the edges.
Screen refresh is slow (but that is inherent in e-ink technology).
On the positive side:
It can read PDFs, and you can annotate them and merge your notes and original PDFs together into new PDFs.
Big screen, so reading papers an the device works pretty well. And it's pretty much like reading on paper. (But physics papers in two column format on big pages can be problematic.)
It uses an SD card for storage. I have a 16 GB card in the device, which is silly given that I have barely managed to put one GB on it so far.
Open software architecture, so third-party software is possible. For example, xournal has been ported to the device. Also, the database format is semi-documented, enabling third party merging software (which is needed because the supplied software is windoze only).
That's a shorter positive list than negative list, but the pluses are bigger than the minuses, so one comes out about even. (Forget what I wrote about conditionally convergent series. It was a joke, but half serious.)
There are lots of other readers on the market, and many more coming, but most of them are geared towards book reading (prose, not science), so they are typically smaller, and many of them have no note taking capability. But more are coming. Hopefully, with time the price will come down and these things will become more attractive and useful. I certainly am hooked, despite the price and the shortcomings.