To update my own original post and in reply to award9051 as well: I opted to reboot our vCenter server this weekend after having so many issues. This is probably the first reboot since the upgrade process itself. Since the time of reboot, everything has been behaving properly and we're not seeing the hung "starting task" situation any longer. I'd cautiously say "problem solved".
Fingers crossed it remains this way.
award9051 - have you rebooted the VMSA since completing the initial upgrade / install?
All of our upgrades are done at this point: VMSA to 5.5, all blades running ESXi are 5.5 and VMWare Tools is on every VM that is capable of supporting it.
- Aaron