A new CraftBukkit Beta Build (1.5.1-R0.2) that provides Minecraft 1.5.1 compatibility as well as stability and security improvements is now available. If you’re running 1.5.1-R0.1, updating is HIGHLY RECOMMENDED.
Will plugins break with this build?
Provided the developers of the plugins you are using are keeping up with the development of Bukkit, all your plugins should work fine, with the exception of plugins that use Minecraft or CraftBukkit code.
What is a Beta build?
A Beta Build is in between a developer build and a Recommended Build. These builds simply work and are promoted much more frequently than a Recommended Build. While we will do some testing before promoting a beta build, we will not be running it through our extensive test process. As such, there are no guarantees that they will not contain minor bugs. If we do find out they are broken, we will mark it as such on DLB and promote a new one. A beta build may contain incomplete API and new features but they should not interfere with running the build in any way.
This particular Beta build has been promoted to provide servers with fixes for some known critical exploits. If you’re running 1.5.1-R0.1, updating is HIGHLY RECOMMENDED.
For more detailed information on what is contained in this update, please see the changelog here.