In general, I feel like I'm going to want a Kindle or something similar pretty soon (so I'm doing the research on them), but with the delays discussed in this thread and a few other minor issues, I think I'll wait a few more months.
Another thing to consider when looking at the Kindle will be what other kinds of books you like to read. I've found www.manybooks.net
to be a great source for Kindle books that are free. They are mostly Project Gutenberg books that are no longer under copyright, and are now available to the public for free. Manybooks has converted the majority of them into Kindle versions that you can download to your computer and transfer to the Kindle, or you can go to their portable website mnybks.net and download the Kindle versions directly to the unit itself, using the Kindle's mini web browser. Obviously, these are older books, but if you're interested in books by Dumas, Lovecraft, Jules Verne, Lewis Carroll, Arthur Conan Doyle, etc. its a great source for Kindle books.
A really really good source of free eBooks for the Sony Reader line (500/505), Kindle, and any other device that reads Mobipocket format is MobileRead http://www.mobileread.com/forums/
because people there have been posting lots of public domain eBooks and freely available eBooks. A lot nicer formatted then the ones Manybooks gives you. There is even one Star Trek eBook available for free.