The above question, or some variation, has come up a few times lately, so let's try to clarify this here.
The SharePoint Conference (SPC2008), which will take place in March 2008 in Redmond, WA is primarily intended for those in IT who use, deploy, and configure SharePoint. If you are focused on SharePoint deployment you should attend the SharePoint Conference. If you are a SharePoint developer you should attend Office System Developer Conference (ODC2008). Although there will be some developer oriented content at SPC2008, ODC2008 will have the deep developer-focused content you would want to know about to develop solutions that not only build on the SharePoint platform, but also take advantage of the other technologies in the Office system.