An article (Google Scholar's ghost authors, lost authors, and other problems by Peter Jacso) published in Library Journal Academic Newswire discusses whether Google Scholar is a reliable tool for citation analysis:
A free tool, Google Scholar has become the most convenient resource to find a few good scholarly papers--often in free full-text format--on even the most esoteric topics. For topical keyword searches, GS is most valuable. But it cannot be used to analyze the publishing performance and impact of researchers.
Google's algorithms create phantom authors for millions of papers. They derive false names from options listed on the search menu, such as P Login (for Please Login).
Very often, the real authors are relegated to ghost authors deprived of their authorship along with publication and citation counts. In the scholarly world, this is critical, as the mantra "publish or perish" is changing to "publish, get cited or perish."
Google Scholar's publication and citation counts, and metadata for bibliometric and scientometric evaluations too often resemble Bernie Madoff's profit numbers. Just as investors preferred the non-existent reality described by Madoff's figures, users may like the publication and citation counts reported by Google Scholar, and the many inflated indicators derived from them.