I got to say Wow! I have been working with Drupal for the past 4 years and translating content has been a difficult process not only when installing a site with different languages but maintaining that site and the translations. Now with Drupal 7 this tasks is becoming a pretty simple task thanks to 2 fully recommended modules:
Localization update module is now taking care of importing the .po files from translations project http://localize.drupal.org/ not only for the core files but the community modules installed on your system, automatically! and something i really find interesting is the ability it gives to sync translations directly with the translations project server. The Localization client will give you a nice on-screen interface that helps translate the strings that belong to the current page you are visiting. There is not way to easily translate Menus yet ( http://drupal.org/node/1104686 ) but creating a block menu for each language will help. Enjoy!
