Microsoft does not have a complete resolution for this problem yet, but they have found some more details. Evidently the problem with SQL Agent failure only occurs on systems using a domain admin account for the SQL Agent Service account. Microsoft is not 100% sure yet, so this is just a preliminary finding. However, it does match my own personal experiences. Worst Practices always has a cost. Several DBAs just found that out the hard way. Just as a reminder, this problem only occurs on x64 clusters using SQL Server 2005 build 3186 and higher.