This new release of WordPress has major focus on Feedburner issue that was in 2.0.6 and the PHP security problem. The release has fixed both these major issues. For maximum security it is recommended for 2.0.6 users too to please upgrade to the latest version as soon as possible
For wordpress users who shall be upgrading from 2.0.6 they do not to update all of their wordpress files. Below is the list of the files that have changed since 2.0.6:
Here is the detailed changelog.