Disaster for publishers is an understatement. Once people get used to seeing full webpages while still on Google they may become alienated to actually visiting those sites. At the very least if you block this feature on your site, and Google shows nothing, visitors may bypass you altogether creating favoritism.
Hate it, enough to ban google from my sites just like any other content scraper. Google has no right to display copyrighted content in full without permission. I'd actually sue them myself over this one. Talk about a "borg" like collective mentality, they spend relatively little on their own content yet use everyone's to make themselves stinking rich!