MySQL released version 5.1.51, this is a bug fix release which also includes some security fixes and it is up to you if you want to upgrade. Check all the fixes and changes that are listed on the release notes to see what issues are resolved and if you are affected. Most of them are about replication which we don’t use in our setup.
If you are still using a 5.0.x version I would urge you to plan a upgrade to a 5.1.x version.
I’ve compiled this version and did some tests on my servers and it worked without any problems.
Read the documentation on how to ugrade MySQL.