The Onion‘s AV Club recently posted a nice overview on MGM musicals. Here’s the AV Club’s definition of their primers:
Primer is The A.V. Club’s ongoing series of beginners’ guides to pop culture’s most notable subjects: filmmakers, music styles, literary genres, and whatever else interests us—and hopefully you. This installment: the feature-length musicals produced by Metro-Goldwyn-Mayer studios during Hollywood’s “golden age.”
Most of the information on Gene Kelly falls on pages 1 and 4.