I used to get quite involved with oaths and fealty and loyalty. True it was mainly for roleplaying purposes but it added a lot of atmosphere if not potential for intrigue and what not.
On the wiki I saved a good chunk of the letters / rp's / oaths. Take a look and see if that's something you liked or could use for inspiration.
Personally I'd hold players / characters to their oaths and treated them accordingly.
http://wiki.battlemaster.org/wiki/Keepers_of_Lore/Regions/GiaskScroll down a wee bit until you hit the text : ''
Listed here are surviving records of the letters and document shared...''