We've got a clustered setup going now.
http://wwrk.maa.org/moodle/mod/forum/discuss.php?d=548
We're using heartbeat/LVS to load balance two webservers and two mysql servers. The mysql servers keep in sync through mysql replication (clustered mysql did not work as it would require schema changes to the webwork databases)
WeBWorK Main Forum
Clustering and High Availability Webwork Servers
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