You can now merge cells in tables in a Google Document. This has always been a feature in Spreadsheets, but it is now available in Docs as well.
This launch adds the ability to merge the cells of a table in Google Docs. Merged table cells can span more than one row and/or column.
To merge table cells, highlight the cells to be merged in your table and select Merge cells from the Table menu (or right click and select Merge cells).
Merged table cells in Word documents can now be imported as well.