I Found This On Bukkit: http://forums.bukkit.org/threads/craftbukkit-1-2-5-r4-0-is-now-available.80036/ 1.2.5 R4.0 Should Be Latest!
Thats good, but EMC does not use CraftBukkit directly anymore, instead we use a Fork called CraftBukkit++ that brings performance improvements. The mob spawn issues are actually a CB++ bug, and not plain CraftBukkit But sadly CB++ has not updated yet: http://build.spout.org/job/CraftBukkit / We could potentially downgrade back to CB, but I don't know if Justin wants to do that. CB++ Did greatly help improve the lag problems.