so far i've found the kindle and ebooks to be quite nice.
i don't know where some have been buying $10-15 paper books - most hardcover books now seem to be closer to $30. in those instances, $9 for an ebook equivalent seems like a decent deal.
i do re-read some books years later - but i think that was to some degree a factor of budget and not being able to afford or justify another $30 book - i'll just re-read this one i originally read a few years ago instead.
prior to the kindle, i'd get rid of accumulated books once a year or so by taking a bunch on vacation and leaving them behind for hotel staff or whomever. donating to charity or to book sales. their bulk is really inexcusable IMHO.
DRM - i used to have an issue with the DRM and was obsessed with finding the reader that best-supported the open formats - thinking that i'd spend all the extra time on the computer tracking down the open books, doing conversions, uploading and downloading, etc. eventually i came around - i really cannot be bothered to spend one more minute on the computer doing that sort of thing - the kindle's disconnection from the computer is it's killer app feature.
sony DRM i would not trust as that company doesn't seem to know what it's doing - they are a hardware company and a content company and quite often create devices that are draconian in the ways they inhibit fair use. the music CDs that cripple your computer, the fiasco with DRM and their minidisc products, their online "stores" and whatnot. I'll personally never buy another sony product ever again, no matter how positively reviewed.
i went with the kindle for two primary reasons - no computer connection required, 200K+ titles available and growing.
the chances of me buying another standard format paper book have diminished greatly. i won't say never again, but there would have to be some strong reasoning for me to consider it.
as to future-proofness. the more successful the kindle becomes, the less risk there is in future obsolescence. likewise, tech accelerates and eventually, there will be a software hack to break kindle DRM, or kindle will do it on it's own as itunes has begun to do... once the revenue stream is established and the risk is minimized and popular culture takes over.
i would be far more worried about sony - they are not in the book business. the chances of their "store" surviving another 18 months are slim IMHO. amazon is positioned very well to crush them if they so choose. sony's hope would be to abandon the DRM and store model and adopt an open-format reader to go against the bebook and iliad and others.