Office Live recommends SharePoint Designer as the premier development tool for building composite applications and enhancements to the Office Live Business Applications.  I think I've mentioned that here before. Well, our friends on the SPD team have created several useful training videos that you should check out.  There are 6 of them.  I think 5 of them are fully relevant to Office Live.  The 6th one regarding the Visual Studio add-ins is not relevant to Office Live because you cannot upload your own custom code.