One of the biggest reason for my Sony purchase is the expandable memory via SD card or MemoryStick Duo Pro. And as another poster said, I use my reader for reading. Nothing else. I browse the web with my PC or laptop. Email? ditto.
Wireless delivery was not a factor b/c I alway have at least my laptop near. Besides, I like being able to shop different ebook sellers for the best prices.
But that's just my 2cents. It just comes down to what features you prefer
Happy shopping!
PS. the huge keyboard at the bottom of the Kindle was a big turn off for me. I couldn't help but think, that space is better used for reading. JMO