Love this idea of writing a heart-felt letter to the mother of the groom on such a special day. When her son becomes your husband, thank her for raising him to be the man of your dreams. I can't wait to write a letter like this to my future mother-in-law!
Assign each table a different anniversary year (i. table 1 would be anniversary year etc.) and let the guests at that table write notes to be opened on that particular anniversary year (a unique alternative to a wedding guest book).