Some rough numbers: bundle install has gone from ~50s to 3s for my Jekyll + s3_website setup. The overall build has dropped from ~120s to 45s thanks to that and using a cached version of Ruby.
One gotcha for anyone with a similar setup: make sure Jekyll's _config.yml is set to exclude/ignore the vendor directory. Oops.
One gotcha for anyone with a similar setup: make sure Jekyll's _config.yml is set to exclude/ignore the vendor directory. Oops.