Today I was in the process of trying to put one of my ESX 4 hosts into maintenance mode. However after about 30 minutes of waiting the task was only 2% complete. Right-Clicking on the task and clicking cancel did nothing to help. So I ran the following commands to kill off each and every task that was stuck or in progress and brought sanity back to my cluster.
service mgmt-vmware restart
service vmware-vpxa restart