New commits are automatically retrieved and stored when consulting the repository in the app. This behaviour can be disabled by unchecking 'Autofecth commits' in configuration settings.
Commits can be fetched offline by running (recommanded at least for the initial import of past commits): 
ruby script/runner "Repository.fetch_changesets"
It will load commits for all of the repositories.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@377 e93f8b46-1217-0410-a6f0-8f06a7374b81