Most of the security flaws fixed were relatively benign in nature, fixing things like browser crashes -- but at least two separate bugs, both present in the Windows version, could result in code execution and system compromise. The mentioned flaws even affect Windows 7.
Overall, the release isn't very exciting, but because much of the changes are related to security, it's definitely worth getting if you use Safari. Apple pushed out the new version for all the platforms they support, including all newer versions of OS X, Windows XP, Windows Vista and Windows 7. There is still no native way to run Safari on Linux, sadly.