Um. Well, things that would make the Kindle more attractive to me would be:
A history of working as advertised and good customer support when it doesn't. Yeah, I realize this takes time. This is actually one major reason I haven't bought it (the other being lack of money on my part).
More formats supported natively. I understand why pdf is hard; keep working on it, because it's important. And epub support shouldn't even be hard. (Supporting the other ebook files out there would widen the available content and reduce switching costs for other users, but aren't a big deal to me in particular because any e-books I have are in formats the Kindle can already use.)
Amazon selling more books without DRM and clearly labeling whether a book has DRM or not. Plus I would like to see Amazon selling e-books to all comers in all formats; I think this is just a good citizenship issue.
Bigger selection in the Amazon store.
Major advances in the design itself (thinking long term here--these are not required to get me to buy it). I'd like to see it with the keyboard replaced by a touch screen with handwriting input (perhaps only at the bottom, like a PDA) so you can get rid of the keyboard and use that space for "reading real estate." I know it's hard to combine e-paper and touchscreen, but iLiad does it, so it must be possible.
Another possiblity that would be cool would be if it would open like a book, with a screen on each side, so that it can fold out flat and display PDFs at 8 1/2 by 11.