I think this is mostly an issue for information sites where simple answers are calculated or pulled from a database--e.g., sites that do currency conversions or supply dictionary definitions, or that give weather reports. And, of course, it's a problem for e-commerce sites that attract users by supplying airline fares or price comparisons. Such sites depend on branding and advertising to bring in users.
But I don't see the search engines becoming competitors of (or substitutes for) sites that deal in human-edited, in-depth information. I can see them competing with template-based, keyword-driven sites where most of the content consists of user-posted reviews or comments and links to other resources. A Google Travel, for example, could be a dangerous competitor to a travel "advisor" site, simply because it would duplicate the latter's strengths: a reliance on automation, traffic, and scalability.
Users already depend on SEs to find specific information. There's nothing new about that. I doubt if most users (other than professionals) have ever sought out links. That doesn't mean they don't use links when they find them. When I was at About.com, a fair percentage of my weekly traffic consisted of "outbound frame" page views. [And no, I didn't approve of About's outbound frames, so please don't take me to task for that. :-)]