Quick suggestion, since having negative honor makes it pretty hard to play (perhaps its just me) I suggest there be some special options unlocked and available when one has enough negative honor.
E.g. When sieging a castle, if there are no lords inside, you normally have the option of meeting the person in charge. With enough dishonor, you can bribe the guard to desert. How much you can spare will be able to soften up the castle quite some. Also, for realism, make it impossible for full desertion since some people are loyal to their lord. (Factors affecting this is player renown, owner's renown, amount offered, persuasion, army size, garrison size, owner's lord type [ cunning, martial, upstanding etc. ], right to rule, controversy) Doing so will cause a spike in controversy and a massive hit to your relation with the owner.
I hope to hear a reply on this from you waihti and if you do like it, i will get to thinking up more stuff dishonorable people can do as added perks.
Honorable people ought to have other perks as well. Maybe some new quests from the King or fellow vassal lords. Perhaps when dishonorable, Kings rarely listen to your counsel while honorable ones get treated like advisors.
Merging this idea with my Lord council meeting can make pretty interesting results.