the success of KOBO and Kindle will depend on two things
1) price of e-reader (I would rate this as "very good" since e-reader is not expensive now)
2) content (we will find out in the coming months how many Major Publishers stay out)
Imagine when Itunes/Spotify debuted, it lacks music from half of the Major Labels. Or when Kindle debut, it lacks ebooks from 3 of the Big 6 Publishers. That would put a significant dent on adoption.