Have a document library using OOB approval workflow
It works properly in Windows XP, but doesn't kick off the workflow when the user is using Windows 7.
HOWEVER, If I add a second content type to the document library and then switch my non-working content type to be the second one in the list (not the default). It miraculously works.
So it's only not working in Windows 7 if it's the default content type. If it's not the default, then it works.
EDIT: This link seems to describe the issue a bit further.. unfortunately no solution for this guy yet either http://social.msdn.microsoft.com/Forums/en-US/sharepointworkflow/thread/fc5e7705-2fc5-4698-865e-c31649851514