We are running Jira on a box under VMware ESX 4.0 and performance is vaiable to say the least. The physical box has 12 Gig RAM and 4x Xeon 2.26 GHz CPUs. vCentre is telling us the CPUs are not maxed out at any time, RAM is fine too. When we issue a request to the host it sometimes maxes out all 4 vCPUs. Sometimes it's quick, sometimes very very slow. There doesn't seem to be a pattern.