We're currently evaluating SDP, and for the most part I like what I see. The one major problem we're running into though is the inability to use the Location field in a business rule.
I understand Departments are tied to Locations, and you can use Departments in Business Rules. But we're also using AD integration, and when you use an AD user as a requestor, you cannot select a department. Most of our users in AD were not entered with departments (we're a school) and thus this does us no good.
So I create a custom field for the request form, for location. That works fine during the request, however you cannot use custom fields in the Business Rules either.