I'm having a similar issue.... no lag with 25 players on hmod, 100% CPU and Awful lag with bukkit... on minecraft 1.3...
Sorry, forgot to mention bukkit build: Crafbukkit version 0.0.0-443-g8f199f7-b420jnks (Build 420 Compiled by Jenkins) --- merged: Feb 25, 2011...
I went from running a 25 player Hmod server, Lag free with no issues, to occasionally being able to play with less than 4 people on...
Edit: Using Craftbukkit latest build compiled by Jenkins Working: AntiGrief (only using the antigrief.prevent.block.ignite node) DeathTpPlus...
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