I think this is an important UI improvement. It is awkward, and counter-intuitive, enough that you need to add people and companies to a deal by using the single field, names divided by commas. But even to review, later, who is associated with a deal you have to "edit" the deal then scroll the cursor through the field to review the other names that don't fit in the small field. In my opinion, there should be a + button to allow you to add people and companies to the deal, one at a time, like adding tags. Then, the header for the deal should list each of these contacts. Really there should also, then, be a way to prioritize the contacts, even if it is just choosing one of the contacts to be the primary contact. But there could a drop down associated with each contact to qualify the relationship... client, partner, colleague, vendor, etc.