Ebrahim Ezzy at the Read/Write Web reviews Search 2.0 engines (Part 1). He categorizes search engines as follows:

What I'm calling Search 2.0 are actually third generation search technologies. To explain the generations:

• First-generation search ranked sites based on page content - examples are early yahoo.com and Alta Vista.
• Second-generation relies on link analysis for ranking - so they take the structure of the Web into account. Examples are Google and Overture.
• Third-generation search technologies are designed to combine the scalability of existing internet search engines with new and improved relevancy models; they bring into the equation user preferences, collaboration, collective intelligence, a rich user experience, and many other specialized capabilities that make information more productive.

Examples: Swicki, Rollyo, Clusty, Wink, Lexxe

Ezzy's review is concise, informative, and worth reading. In Part 2, he plans to review other search engines and ask these questions:

How is traditional search evolving to Search 2.0? Can Search 2.0 replace Traditional Search, ever?

The answers to these questions may help us in deciding how to help our students improve their research skills.