The changes are primarily interface tweaks in Buzz's privacy settings. Google has worked to ease collective privacy concerns. No doubt, Buzz will continue to evolve as Google seeks to attract users from Facebook and Twitter to its own hive. Here is Google's punch list for this round of changes:
*More visible option to not show followers/people you follow on your public profile
*Ability to block anyone who starts following you
*More clarity on which of your followers/people you follow can appear on your public profile
You can read about these changes in detail at Google's blog.