One factor nobody's mentioned... if you're an impulse buyer, like me, you don't benefit from wireless making it so easy to buy on impulse. One reason I chose the Sony Touch 600 is because it does NOT have wireless connectivity, which protects me just a little bit from myself.
I'm retired, and almost all the books I read are free, or from the local library's eBook collection. How would wireless benefit me? I don't think it would. But for those who want it, and can afford to buy ebooks, it's great.
(To stay on-topic... I tried the Kobo also, but preferred the more solid substantial feel of the Sony. The Kobo felt a bit flimsy to me.)