Well, if you make a backup of a Moodle course, then you get a zip file. In the zip file, there is a moodle.xml file that contains all the data from the database in a fairly sensible format, and then any other files that relate to this course.
Therefore, you can get all your data out of Moodle in a format that other systems can quite easily process. However, working out how that data corresponds to the particular features of a particular other system is not really a Moodle-specific question.
And, we are aiming at IMS Common Cartridge export in Moodle 2.0 which should help with this sort of things, but Moodle probably has more features that CC supports.