Like manay organizations, we have a Direct and a reseller Channel (Agents, Private Label partners, Wholesale partners). The Channel Agents use a Partner portal that is based on SFDC. These Agents often input Leads into the system so that we can help our partners market to them. When we were using Genius.com, segmenting them was a simple matter of saying whether the "Owner's Role" contains or does not contain "Partner". I could, if I needed to, use the Owner's Profile as well. Both of these fields were set up specifically for this purpose in reports and campaign lists.
How do you go about performing this segmentation in Marketo?