[BoldlyDubious]

I have bought an Asus DR-900 a couple of weeks ago. It's my first ebook reader. I would like to offer my own thoughts about it, in return for all the useful information that I got from MobileRead users in the past months (when I was lurking around). In particular, many thanks to Marcor, who posted a thoughtful and balanced review of the device.
Now, to my own review.

First: the Sipix screen. Yes, its background is decidedly grey. It's noticeably greyer than Vizplex E-Ink screens (which are greyer than Pearl ones). I was worried about this, actually. However, I have used the DR-900 in a wide set of lighting conditions, mostly to read pdf files with small print (arguably the worst case), and I don't think this is really an issue. Reading is pleasant, and characters are crisp in their strange dark-gray-over-light-gray appearance. I'm starting to convince myself that the "need" for a white, or whitish, background is mostly conditioning from the long use of white paper...
Screen refresh is slow; slower than E-Ink, I think. In addition to that, the processor seems to have been optimized for minimum power usage, i.e., to be barely sufficient. So, it's true that if you are impatient (e.g., if you press many times a "turn page" button) you can easily choke the CPU: it seems that queued commands are not forgotten, but they take a few seconds to be executed.
This makes the experience of reading on this device all the more similar to reading paper books. In comparison to using a PC, everything is slower, less interactive... and ultimately more relaxing. This is not bad, after all :-)

That said, you can forget being able to jump quickly from point to point of a text. (So: no easy reading of scientific papers, for instance, unless you never feel the need to check a formula, definition or reference). This is a device sharply focused on one task: sequential reading. Annotation functions, while existing, are -in my view- too slow to be really useful. More generally, the on-screen keyboard is usable but not really practical for frequent use. On the other hand, the dictionary works well (I use it only occasionally, so slowness is not an issue here) and the text-to-speech functionality seems to work pretty well.
The capacitive touch screen is very good. Its presence means that the device is not much bigger than the screen itself, which is a big bonus (the Kindle DX is really too large, for instance). The main operations (e.g. page turning) can also be performed using the physical keys, so the choice is up to you. By the way: in the box you find a very good cover for the DR-900, sturdy and reasonably good-looking. Downside: it's very heavy, almost 200g (which means that you are have to lug something like 650g... not yet netbook territory, but pretty heavy nonetheless).

For the time being I have only really used the device to read pdf files. I also tried epub, html, and txt files: they all seem to be reasonably well supported, although the device gave an error while reading the very large html file of a novel. The pdf reader has the bare minimum of functions. In particular, the zoom has (few) fixed levels, does not go over 200%, and you cannot crop the margins. You can pan around with your fingers (good), but you will have to wait the usual second or so for the screen image to be redrawn. For most A4-formatted documents you can find a reasonably comfortable setting, but I have not been able to read a newspaper on it (print is too small at 200%). If you are looking at the first part of a page, "page down" takes you to the first part of the next page, NOT to the second part of the current one. Sigh. On the other side, the device remembers zoom setting and pan while changing page.
I now use pdfcrop for Linux to remove margins from pdfs before transferring them to the DR-900, then visualize the pages at 100% zoom: in this way I usually do not have to bother with panning.

Wireless connectivity is limited to networks which broadcast their SSID. Web browsing is nothing more than rudimentary. Barely usable, actually: extremely slow, bordering on the "is this thing still working?". Rendering of simple HTML pages seems good. With the last version of the firmware (394) the browser inexplicably works with the screen in portrait position, which of course is not the right form factor for the web. To sum up: you *can* browse the web if you are desperate and there is not a PC within 10 minutes of walk, but only in that case. And you will swear not to do it again.
The RSS reader is a very good idea; unfortunately, it seems to be at the same development stage of the browser (which I would define as "early beta").

You can download files from the internet (I tried this with my Dropbox repository). They are put in the device's own flash memory, but you cannot choose where. Actually, there's no way to organize the contents of the internal flash memory, or even to delete files, without using an external PC. The same is true for the contents of the microSD card. In theory, you can use very large SD cards (up to 32GB, I think). In practice, the device consistently hungs (System Error 11) while trying to index large libraries, which is absurd. The best I managed to do is putting 700 files (organized into directories) on the microSD. So, good-bye to my idea of keeping my whole library on the DR-900 :-(
The device allows navigation among directories, although you have to put all of your ebook files in a top-level directory called "book".

I tried the other functions (music player, ...) only briefly; they seem to be rather primitive as well. For example: you can draw (with your finger) and save sketches: but you cannot erase wrong lines, and there is only one line thickness available. Very very basic indeed.

Let's conclude. Notwithstanding the many defects that I described above, I quite like using my DR-900 for reading. Reading is easy and pleasurable, at least when the available view options are suitable for your particular file: nearly at the same level of a physical book (high praise indeed).
Most of the issues I pointed out seem to depend on the firmware alone: I warmly hope (for me and for Asus) that they will be fixed soon. If they will be, the DR-900 will easily become the best general-purpose e-reader on the market.
With the current firmware, the DR-900 is a very good reader for books (with the key feature of a large screen) but nothing more. Every other function seems to be in beta version or worse. The firmware is ridiculous in comparison to more developed products like Sony's PRS series; in particular for what concerns handling of pdf files. Which is a shame, because easy reading of pdf files is the main reason for buying a large-screen ebook reader such as the DR-900.

By the way, I tried to download the GPL-licensed code from Asus Support to take a look at it, but "strangely" the download links doesn't seem to work. Is Asus trying to prevent us from seeing how many TODOs are scattered through the code?