Over night, I've upgraded the server to use Percona Server as a replacement for MySQL. It's a direct replacement, and offers much better performance over the standard MySQL offering, especially for the database we are using for the forum (InnoDB)
http://www.percona.com/
Percona Server is an enhanced drop-in replacement for MySQL. With Percona Server,
Your queries will run faster and more consistently.
You will consolidate servers on powerful hardware.
You will delay sharding, or avoid it entirely.
You will save money on hosting fees and power.
You will spend less time tuning and administering.
You will achieve higher uptime.
You will troubleshoot without guesswork.
Does this sound too good to be true? It's not. Percona Server offers breakthrough performance, scalability, features, and instrumentation. Its self-tuning algorithms and support for extremely high-performance hardware make it the clear choice for companies who demand the utmost performance and reliability from their database server
I've been running it on the backup server, and haven't seen any issues, updated on the live server this evening.
Server version: 5.5.21-55-log Percona Server (GPL), Release rel25.1, Revision 234
As always, any issues, let me know.