Anyway, it turns out that the problem is far too many don't use google, and most other search engines really suck. People are idiots and don't use phrase searches (putting quotation marks around their phrase). Google is smart enough so that if you don't put quotation marks in, it still puts phrase matches first in the sort order.
Anyway, from looking at the referrer logs, the NaNoWriMo novel hits are about 20% search engines, and 80% hits from IE 6 with no referrer at all (has IE started not sending referrers?), so probably those are all searches too. And since the novel is 50K words, and most of my other pages are much shorter, if a random search is going to hit any page on my site, it's likely to be that one (just because it's got more words that'll match). So... random.