The use of search engines for academic research has divided libraries and the academic community. Google is the search engine most single out as representative of what is good or bad with search engines in general. So though much of what is said below may be directed specifically at Google, it may also be applicable to any other internet search engine.
Search engines are an indispensible research tool, but should be used primarily as a tool, that is, as a means of getting (often unvalidated) contextual information that can then be used to do more in-depth research using scholarly sources (which are generally available through library gateways - e.g. library catalogs, indexes to scholarly literature, etc.)
Search engines are great for quicky (and preliminarily) verifying common facts (names, dates, locations, etc) or even the spelling of words or names. Obviously search engines do not verify the validity of those sites/facts to which they provide access. At best, they use sophisticated algorithms that "validate" or rank each site using usage and its association with other high-use sites. As such, facts "verified" using Google, or other search engines should always be double-checked using a reputable source (whether in print or online).
Because most search engines now use algorithms to sort their results according to usage and association with other high use sites (among other things), the rankings they provide give a snapshot (however blurry) of how other internet users and website creators "value" these same sites.
Google and other search engines are beginning to provide access to sources previously accessible only to stand alone search systems, like library catalogs, indexes & databases. At the present, however, only your library can give you full access to hundreds of commercial research resources.
What is "Google-able"? (how much of what is out there).
What is not "Google-able"?
Free/Accessible; Free/Inaccessible; Fee-based
Algorithms vs. Meta-data; is there a happy medium?
What is weighed more heavily and why?
Wildcards and Boolean logic.