Which PowerCLI version are you using ?
Do a
Get-PowerCLIVersion
For me this works with PowerCLI 5.0.1 against a vCenter 5.x with only the Get-Cluster for the entity.
The Get-VIEvent cmdlet becomes slower depending on the number of objects you pass via the Entity parameter.
I notice a that it runs twice as long when I do 'Get-Cluster MyCluster | Get-VM'