I have a Sony PRS-505. It works reasonably well for reading straight through, but is too slow for jumping around comfortably. It can read PDFs directly, but cannot zoom (increasing font-size will reflow the text to fit the margins which actually works pretty well for text only PDFs but messes up formulas and diagrams). You can rotate the view 90 degrees which leaves the text a decent size provided you chop off all the margins before putting the PDF on the device. Adobe Acrobat (full Acrobat, not the Reader) can do this, or a variety of commandline tools: on Linux you can use pdfcrop, pdftk or pdfmanipulate (that last one comes with calibre), a windows program called soPDF I found on some ebook forum, etc. Removing the whitespace in the margins really improves the experience, and should probably be done with any of the current eBook readers: even the ones with zoom will probably zoom very slowly.