Highly recommend Documentum. I just finished writing a white paper on the ROI for our company's implementation between SharePoint and Documentum. Documentum comes out so far ahead in three and five year ROI figures it's not funny.
I always hear that Documentum is expensive, and at first glance it appears to be. However, considering that you get a true *and* complete enterprise content managment platform, you end up paying up front for what you need. SharePoint is a full-featured collaboration platform and a *basic* content managment system. Cheap at first, but you end up paying extra for third-party content and support for what you need later. SP is fine for some small companies, but it simply does not scale.
SharePoint is fine for departments to use for project management or collaboration. Anything else, including business process management, and you're going to pay for it later. If your IT wants to use it, that's okay as long as you have something else like Documentum, FileNet, or Alfresco to fill in the gaps.