You should be able to have look and feel of a Sony in a store (not sure which ones in the US do them, sorry), and I've read here that Amazon do a 30 day return on the Kindle (you need to pay return postage) so you could have a lok at both and see which one feels and looks best for you.
You can buy ebooks outside of the official stores - places like booksonboard.com and fictionwise.com are popular.
It might be worth working out how many books for the Kindle you can buy before the $100 price difference is irrelevant - if it's more than you'd be likely to buy over a reasonable (you need to work out what's reasonable for you!) period, then personally I'd be tempted to go for the Sony and spend the difference straight away on books
