Plugin to Retrieve Current Business unit - CRM 2011

public void Execute(IServiceProvider serviceProvider)
    {
        IPluginExecutionContext context = (IPluginExecutionContext)

serviceProvider.GetService(typeof(IPluginExecutionContext));

        //get initiating user (or impersonated user)
        Guid userId = context.InitiatingUserId; //or context.UserId

        //set up OrganizationService
        IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
        IOrganizationService service = factory.CreateOrganizationService(userId);

        //retrieve user record
        ColumnSet allFields = new ColumnSet() { AllColumns = true };
        Entity user = service.Retrieve("systemuser", userId, allFields);

        //get business unit lookup
        Guid businessUnitId = ((EntityReference)user.Attributes["businessunitid"]).Id;

        //optional
        Entity businessunit = service.Retrieve("businessunit", businessUnitId, allFields);
    }