I am a very happy Scribd subscriber. I looked at the cached links Julie posted and to be honest, it isn't in any way a danger to Scribd if that is what will be in KU. Content is king and no offence, I wouldn't pay $9.99 a month for pretty much only self published titles and then the amazon imprints. That's is what is in the KOLL right now. I am working my way through the Amazon Montlake titles each month with my Prime.
On Scribd I get HarperCollins, Kensington, Simon and Schuster, Sourcebooks, Open Road Media, Diversion Books, DreamSpinner, etc. In addition to many self published titles through Smashwords and D2D.
I browsed through the selection on that link and I could barely find stuff I either didn't already own free, or already have read through my KOLL. I would have to read 4-6 book a month on the service to make it a good deal. I have no lack of selection on Scribd.
But I'll keep my eye open and if they can get some big publishers it would be a competition. But considering how the relationship between Amazon and some publishers is, that is highly unlikely.
But overall I have seen a huge interest of readers in these services.