I have both the Kobo wifi and the Kindle 3.
However, when Kindle enables library borrowing (soon I think), I will most likely use it exclusively. Only got the Kobo for that reason.
All things being equal (library borrowing wise
I would spring for the extra $20 and buy the Kindle.
I have had the Kobo for about 5 months, and already the blue button is separating (noticably) from the unit. Also, as others have noted on here, the page turns are pretty darn slow! There is also some aggravation regarding powering down. Half the time it will not go all the way back to the off screen (goes to the screen saver), so then you have to wait for it to go back to the books, and try again. THAT is even more aggravating to me that the slow page turns. I read to the last minute before work, and shutting down promptly is driving me bananas!!!
Oh, sometimes when I shut down, the screen shows half on and half off, part of the book I'm reading, a wide black line, etc.
When you turn the Kindle off, it goes off!