We have a SharePoint farm patched to Service Pack 1 + June 2011 CU. While going through the ULS logs, I noticed the following error, which is associated with our Metadata content hub site.
Failed to process hub site http://sharepoint/metahub: The changeToken refers to a time before the start of the current change log.
This error would appear once every 15 minutes.
As it turns out, this is a known issue and Microsoft has released a hotfix. Note that this hotfix is included in the August 2011 update.