Most of the time to get to SDN, my starting point is the SAP Service marketplace. I take advantage of the SSO functionality, plus spend a lot of time in the marketplace as well. I have noticed two things there that would be helpful in SDN:
1. Provide a link back to the main SAP Service Marketplace page. The marketplace has this with their "Other Portals" link.
2. When Searching SAP Notes, there is a small box that allows you to do an SDN search. Maybe it would be helpful to provide just the opposite in SDN. A link to SAP notes search from the SDN search.