After a very successful drush code-sprint at BADCamp 2014, drush make now supports YAML format!

Instead of the old INI format

api = 2

; Set contrib directory.
defaults[projects][subdir] = "contrib"

core = "7.x"
projects[drupal][type] = "core"
projects[drupal][version] = "7.32"
; Remove scary ajax error when autocomplete terminates: https://www.drupal.org/node/1232416#comment-8748879
projects[drupal][patch][] = "https://www.drupal.org/files/issues/D7-fix_autocomplete_terminated_error-1232416-179-do-not-test.patch"
; Ensure plain text fields evaluate line breaks.
projects[drupal][patch][] = "http://drupal.org/files/text-plain-1152216-24.patch"

projects[addressfield][version] = "1.0-beta5"

projects[addressfield_tokens][version] = "1.4"

projects[admin_views][version] = "1.3"

projects[field_collection][version] = "1.0-beta7"
; Field collections are ownerless https://drupal.org/node/1954124
projects[field_collection][patch][] = "https://drupal.org/files/issues/field_collection-ownerless_fields-1954124-23.patch"
; Fixes fatal error in migrate code: https://www.drupal.org/node/2315921#comment-9028779
projects[field_collection][patch][] = "https://www.drupal.org/files/issues/migrate-fatal-error-2315921-01.patch"

YAML can be used with the latest version of Drush 7:

api: 2

# Set contrib directory.
defaults:
projects:
subdir: "contrib"
core: "7.x"
projects:
drupal:
type: "core"
version: "7.33"
patch:
# Remove scary ajax error when autocomplete terminates: https://www.drupal.org/node/1232416#comment-8748879
- "https://www.drupal.org/files/issues/D7-fix_autocomplete_terminated_error-1232416-179-do-not-test.patch"
# Ensure plain text fields evaluate line breaks.
- "http://drupal.org/files/text-plain-1152216-24.patch"

addressfield: "1.0-beta5"
addressfield_tokens: "1.4"
admin_views: "1.3"
field_collection:
version: "1.0-beta7"
patch:
# Field collections are ownerless https://drupal.org/node/1954124
- "https://drupal.org/files/issues/field_collection-ownerless_fields-1954124-23.patch"
# Fixes fatal error in migrate code: https://www.drupal.org/node/2315921#comment-9028779
- "https://www.drupal.org/files/issues/migrate-fatal-error-2315921-01.patch"

Included .make files whether local, or discovered recursively within downloaded projects, can be in either YAML of INI format.

In order to use the newly-supported YAML format, simply name files with a .yml extension, such as my_project.make.yml.

The best part? This can be used now! Even though YAML files are mostly a new concept for Drupal 8, drush make will parse YAML make files for Drupal 7, and even Drupal 6.