theme_links() now allows more targeted overrides

Modules can now specify a more specific theme callback for links, so that theming of links can be overridden for specific purposes.

For instance, the Node module uses 'links__node' rather than just 'links' as its theme callback when adding links to nodes, so if you want to override just the theming of these links, you can do it in a mytheme_links__node() function, rather than adding some complicated logic to the the generic mytheme_links() function.

Other examples in Drupal core are links__contextual, links__system_main_menu, links__system_secondary_menu, etc.

(copied from http://drupal.org/node/254940#theme-links-specifics )