Update: Merging Cells directly in Google Docs is now possible - feature update Dec 2014. On of the most requested features in Google Docs is the ability to merge tables. This is not directly possible at the moment, but it is possible in Slides, Sheets and Drawings. As you can insert Drawings into documents, you can insert tables with merged cells. Not the direct method we might like, but it does introduce you to one of the many funky things you can do with drawings. Quick video demo below.