Amazon made the big leap today with their app, including an instant dictionary feature that works fairly well (although not as good with long definitions). With all the changes going on with these apps, Apple and Amazon have clearly established themselves on the top of the heap. Apple has the style, and Amazon has the selection and generally more favorable prices.
Stanza, Kobo, and B&N just aren't in the same league right now. And where on Earth is Sony in all this?