hey monkey,
well, if you search around SDN, you'll see that the whole letter of interest/letter of intent deal has pretty much 2 schools of thought. Some say they help, while others say they doesn't even matter.......personally, I sent in letters of interest to one school and letters of intent to another school that I was waitlisted at, and I never ended up getting off of those waitlists. Yet despite my experience, I still think that letters of interest are good. I think its a way to refresh the adcom's memory of you, while allowing you to reiterate your interest in the school and tell them about your recent accomplishments. A lot can happen in the 4 months + that you are on hold, and so long as you take the time to write a genuinely sincere letter, I think it can only help you out.
As far as what to write, I would include why you liked about the school, how you think the school fits into your short and long-term goals and ambitions, and what you can bring to the community at KU. As stated above, a list of recent accomplishments and grades would be good to include as well. The rest is up to you. Think about it: if you're gonna wait 4 months, you might as well take an active role.......what else do you have to do????