To change Gravity isn't just a "good idea." It's the "law." to Gravity isn't just a ``good idea.'' It's the ``law.'' type
:g/$/s/"\([^"]*\)"/``\1''/g
The following will find words that begin and end with a vowel:
/\<[AEIOUAEIOU][A-ZA-Z']*[AEIOUAEIOU]\>