As announced last year, Google Scholar searches now include legal opinions from U.S. federal and state district, appellate, and supreme courts. An earlier review said that it would not replace commerical case law providers but that it does offer is an amazing place to start case research. A new review echoes those findings:

• Google Scholar: A New Way to Search for Cases and Related Legal Publications, By David Tsai and Courtney Minick, LLRX (December 30, 2009). [Previously Posted by: The Bar Association of San Francisco, republished with permission.]

...Google Scholar will not replace commercial legal publishers such as LexisNexis® or Westlaw® any time soon. The value in paid services lies mostly in the editorial work they provide on top of caselaw -- e.g., headnotes and cite checking features...

Something else to keep in mind -- Google Scholar is limited to case law, and does not include statutes or regulations...

All together, many lawyers have concluded that Google Scholar is a great place to conduct preliminary research, or to review new cases that have not yet been affected by precedent.