I tested the DX on PDF documents, postscript won't work. I chose papers from STOC, CACM, Springer and Elsevier journals, ECCC, my own PDFlatex generated papers and the open access Theory of Computing and the ACM Transactions on Computation Theory journals.
The math looks great. The resolution (1200x824) looks fine, the formulas and diagrams show up as good as on regular paper. No color but that's not an issue for most of our papers.
The papers take a couple of seconds to load and usually (but not always) quick to change pages. I had the worst experience on a scanned paper (Valiant's permanent paper) which took a very long time to load and change pages and looks as lousy on the Kindle as it does printed.
There are two ways to view a paper: portrait and landscape. Let me discuss each separately.
Portrait: A page of the PDF is filled into the screen area. The screen is about 3/4 the height and 2/3 the width of the US standard 8.5x11 paper so some papers are slightly squished, particularly multicolumn STOC and CACM papers have this problem. The ToC and ToCT papers looked the best. The text, formulas and diagrams are also shrunk but still quit readable as long as I am using my reading glasses (yes I've gotten old).
Landscape: You get to landscape mode simply by turning the screen (or manually with the Aa button). The landscape mode keeps the original aspect ratio but you only see part of the page. The width of screen in landscape mode is about the same as the width of regular paper so the type size is about right. You can move through the rest of the page with the Next Page/Prev Page buttons but otherwise no scrolling. The 5-way button seems to have no effect on PDF documents.
Extras: You can do a basic text search within a PDF document but not between documents or in scanned documents. Unlike normal Kindle documents you can't change the type size, add notes, highlight text, convert text to speech or move to a word to get its definition. You can bookmark a page but otherwise the only way to navigate is via the next page/prev page buttons. No way to click on links within a PDF file.
You can move documents quickly through the USB cable. The Kindle has tons of memory and can hold lots of PDF files. You can move whole directories but the Kindle flattens them out listing every file (by file name) separately on the main home page. You can also email papers at $0.15/MB and most of our papers are well under a megabyte.
Many of the issues above could be fixed by software updates but no guarantees Amazon will do so. Also it shouldn't be hard to produce DX-friendly PDF documents, with the right aspect ratio and large font size. If the DX gets popular than publishers might start producing Kindle-friendly versions of their papers. The old Chicken v. Egg problem.