For all who are using to a 5.1.x version. This is a security and bug fix release and it is up to you if you want to upgrade. There is a three security issues mentioned in the release notes. Check all the fixes and changes that are listed on the release notes to see what issues are resolved and if you are affected.
I’ve compiled this version and did some simple tests on my test servers and it worked without any problems.
Read the documentation on how to ugrade MySQL.