We run a Minecraft server with around ~10 people online in the day. We updated to pre-release 5 since everything looked good in it, not critical bugs.

It was OK to start with but after a little while we started experiencing really bad server side performance. I made sure no one was doing anything stupid in the game that could cause lag and then restarted the server. This didn't help.

Finally, I downgraded back to pre-release 2 (we have no command blocks). Load went back to normal straight away.

Happy to provide any further information as needed. Our server performance graphs can be found here. The most interesting one is the CPU graph. I've also attached a picture explaining it.