Google Scholar's court opinion coverage is limited to:
Google does not make public from what vendor they get their case law, but it appears to index opinions from FDSys at least.
Google Scholar for case law is most helpful to use after you have already surveyed secondary sources, statutes, and regulations on your topic, but before turning to licensed databases such as Lexis and Westlaw for case law.
Especially when you are unfamiliar with a particular subject, this easy to use resource allows you to perform an unlimited number of searches to get a sense of the keywords used in legal opinions regarding your subject and take stock of what cases are on point, if any.
Looking for case law on Google Scholar is basically a matter of playing around with different natural language keyword searches.
After finding a case on point, you still need to Keycite or Shepardize it to see whether the case you found is still good law.
Google Scholar offers a "My Library" feature for saving search results. Once you’ve logged into Google Scholar, if you click on “My library,” you should see a “Manage labels…” link which serves as a folders feature. To put an item in a label/folder:
There’s still no folder sharing capability nor does this feature exist within Google Books.
Strengths: Free, easy to use, and no login required.