With each transition the new overshadows, but does not entirely eliminate the old.
Yahoo!
First it was the portal. The internet was small, there wasn’t much information and people wanted to see everything that was the internet. Thus portals were created. They pretty much contained all there was to see.
But the internet grew and portals became unwieldy. Search engines became necessary to sort through all the content portals could no longer contain. This marked a decline in portals.
People are now tired of searching the internet all alone, and want to know that other people are also surfing and whatnot. Social networking sites are overlaid on existing websites to create a social, interactive component.
As for search engines, there is still so much that can be done to improve them. While the above are trends that encompass the entire internet, there are also trends within each of these individual categories.
Search engines are ever so slowly undergoing a transition. They are becoming smarter in the sense that they understand what you are searching for. Now you can type “weather”, for example, and Google won’t just give you results, but it will display the actual weather in your area based on your IP. Wolfram|Alpha is an example of an attempt to create search engines that provide accurate answers to what you are looking for. But the weather example is just the most basic example of what could be carried out on an even grander scale.
Why will this happen? While there’s lots of great content online, there’s also far too much garbage and with SEO, the system can be gamed. This means users are not getting what they want. For common queries, expect to see search engines generating their own results that dominate the page, rather than having third party results as is currently the case.