"Why Our School?"
Often the most important "extra question" on the application is, "Why do you want to attend our law school?" As schools jockey for position in the US News Rankings, this question has become ever more prevalent. If you don't have at least one number above the school's medians, you MUST have a good reason for attending. A vague or superficial answer to this question is a good reason for rejection.
A question about your interest in a school should be given careful consideration and an honest answer. If geography, demographics of the student body, or special facilities influenced your decision, say so. Recommendations from prelaw advisors or current students are also reasons worth noting.
You might also use this opportunity to present a consistent message. If your undergraduate interests included international law, a special program offered by the law school could be mentioned. No matter what your reasons, an honest answer is the best. Reputation, convenience, desire to relocate, can all be mentioned, especially if your file supports this. But beware of overgeneralization or flattery. Writing to Michigan about its excellent reputation is fine (although surely you have something more to say about the programs Michigan offers). The same statement about reputation might seem artificial on an application to Michigan State; in fact, they might wonder if you've confused the two schools.
At wait list time, a statement of interest in the school could make an enormous difference. Many schools that do not ask the question on the application will value the information nonetheless. However, generic or uninformed statements count as no statements. So if you're going to try this strategy, be prepared to tell them a good deal more than their US News ranking.
"You're My Number One Choice"
Applicants labor under the delusion that these words will sway the admissions committee in some way. This is laughable at the national-level schools; isn't Harvard everyone's first choice? And if not, wouldn't almost everyone say it anyway?
Assertions like these must have some weight behind them -- discussions of family in the area, close friends who are current students, special programs that you're interested in. Note that a program that virtually every law school has, like a public defender's clinic, is a bad program to mention. What makes THIS school special to you? If you really can't answer that, you probably really shouldn't be applying there!