When you install Office 2010 SP1, SharePoint Workspace 2010 is automatically installed whether or not it was part of the original installation of Office 2010. This is due to a bug that triggers the installation of SharePoint Workspace 2010.  For more details and to learn how to handle this, see When you install Service Pack 1 (SP1) of Office 2010, SharePoint Workspace 2010 is installed.

UPDATE 3/29/12

As stated by Jonathan in the comments:

Just released

support.microsoft.com/kb/2598245

Issue that this update fixes

When you install Office 2010 SP1, SharePoint Workspace 2010 is installed. However, SharePoint Workspace 2010 is not included in the original Office Professional Plus 2010 installation and should not be installed. In certain situations, Microsoft Office Groove 2007 is upgraded to SharePoint Workspace 2010 when you install Office 2010 SP1. For more information about this issue, see the following Microsoft Knowledge Base article:

http://support.microsoft.com/kb/2612800 Office 2010 SP1 installs SharePoint Workspace