When Search Engines Become Answer Engines [Alertbox]:
This changing behavior is explained by information foraging theory: the easier it is to track down new resources, the less time users will spend at each resource. Thus, the increasing improvement in search quality over time is driving the trend toward answer engines. ... Finally, Web browsers' despicably weak support for bookmarks/favorites has contributed to the decline in users' interest in building a list of favorite sites.
In short, users aren't particularly loyal to sites anymore; and they don't bother maintaining large bookmark lists anymore. Instead they rely on search engines to find the answer to the exact question on their mind at the time. Our attention spans grow ever shorter. We've become information sluts - we don't care where we get the info, or how. We just want it right now, from whoever is willing to give it up.
A creeper issue is that the faster you hit a site and grab information, the less evaluation of that source you can do. So you're not reading over the site to get a good feel for that site - do they know what the hell they're talking about? We don't really check.