Your question seems more philosophical than technical. In truth, nothing of significance changed in ArcSDE between ArcGIS 9.3 and 10.0. The ArcGIS geodatabase metadata was completely redesigned, with an increased emphasis on Direct Connect, but that just furthers the transition of ArcSDE from product to technology started back at ArcGIS 9.2. You're also working at a serious disadvantage by upgrading so late from 9.x to 10.0, since ArcSDE itself is at the cusp of disappearing completely at ArcGIS 10.3.
If you want to get ahead of the curve, you can start by erasing "ArcSDE" from your vocabulary and replacing it with "ArcGIS" or "enterprise geodatabase". That would morph the question into: "What are the differences in enterprise geodatabase implementation between ArcGIS 9.3 and 10.0?", for which you already have an accepted answer.