User Role Editor has Multisite capability.

And from the changelog:
3.6 = 30.04.2012
- WordPress multi-site: when new blog created default role setting is copied for it from the main blog default role value now.
3.5 = 19.02.2012
- User Role Editor could be available now for single site administrators (Administrator role) under multi-site environment. You should define URE_ENABLE_SIMPLE_ADMIN_FOR_MULTISITE constant in your blog wp-config.php file for that. Insert this line “define(‘URE_ENABLE_SIMPLE_ADMIN_FOR_MULTISITE’, 1);” there, if you decide to give single site admin such opportunity.
3.2 = 25.07.2011
- If you run multi-site WordPress network, User Role Editor will automatically duplicate all roles from the main blog (blog with mininal ID) to every new created blog.