There have been a quite a few “URGENT”/”HELP!” threads at Moodle.org recently which all refer to difficulties users have had in upgrading from Moodle 1.9+ to Moodle 2.o. While the Moodle code was released generally to the public and is listed at stable the Moodle docs are explicit in asking all users to refrain from upgrading a production server to 2.0 before it’s first tested to ensure that the the upgrade will work as expected without any hitches or errors.
Certainly there are many benefits of upgrading to Moodle 2.0; however there is a grave risk that upgrading without testing could cause irreparable damage to your existing site.
For more information please visit http://docs.moodle.org/en/Upgrading_to_Moodle_2.0 (Do’s and Don’ts of upgrading to Moodle 2.0).
If you have any questions about upgrading to Moodle 2.0 for any site you might also connect with someone in the forums.