If you are working in a field where new materials are being published regularly and where there's some sense that collecting and reading the whole canon of that field is key to your efforts, portable electronic document readers are appealing. They offer the illusion that your entire research library - at least the portion of it that matters - can be with you everywhere.http://vielmetti.typepad.com/superpatron/2008/10/arxivmobi---phy.html
Although Tungsten T3 was costly, I neverregretted that purchase. The thing turned out to be reliable (in fact, it is still with me, it works fine after 8 years of rather extensive use). I have read thousands of e-books and papers from arxiv.org on my Palm.
If you read further you see lots of discussions of how to convert materials, primarily complex PDFs downloaded as preprints from the net, to formats suitable for use on handheld machines. The Kindle gets low marks for its ability to handle any kind of open formats, and the Kindle 2 is better but not enough better to make it an easy choice for arXiv readers due to limits on its PDF import and conversion process.