Don't know if this is already implemented within ZB, so if it is, sorry.
Placement: Footer
Disable Double Posting for all:
<script src='http://divinitycoding.net/scripts/disDoublePost.js'>
/* Disable Double Posting by Eureka of Divinity Coding [http://divinitycoding.net] */
</script>
Now that seems harsh to disable double posting for everyone including admins and mods, so I decided to code up one for only members 
Disable Double Posting for members only (Members meaning non-staff members)
<script src='http://divinitycoding.net/scripts/disDoublePostMem.js'>
/* Disable Double Posting (Members) by Eureka of Divinity Coding [http://divinitycoding.net] */
</script>
Updated: Disable certain groups from double posting
<script>
/* Disable Double Posting (Groups) by Eureka of Divinity Coding [http://divinitycoding.net] */
var ddpg = ["Members","Moderators"];
document.write('<script src=http://divinitycoding.net/scripts/disdoublepostgrouppost.js><\/script>')
</script>
Edit the red text to group names or add more. NOTE: THIS IS CASE-SENSITIVE.
Updated: Disable certain members from double posting
<script>
/* Disable Double Posting (Certain Members) by Eureka of Divinity Coding [http://divinitycoding.net] */
var ddpm = ["test"];
document.write('<script src=http://divinitycoding.net/scripts/p378/disDoublePostSelMmbrs.js'><\/script>')
</script>
Edit the red for member names. You can add more if you want. NOTE: THIS IS CASE-SENSITIVE. This code is a burden to manage because you have to update it everytime he/she changes his/her name. Of course you shouldn't accept their request if you are to prevent them from double posting as punishment.
Enjoy
"The competent programmer is fully aware of the limited size of his own skull. He therefore approaches his task with full humility, and avoids clever tricks like the plague."
"Program testing can be used to show the presence of bugs, but never to show their absence!"
"APL is a mistake, carried through to perfection. It is the language of the future for the programming techniques of the past: it creates a new generation of coding bums."
