Some sites and types of products are mostly seasonal, and sleepers the rest of the year. For those, the logs are packed for a few months before the fall/winter holidays. There were words and combinations used pulled from some obscure words being used on a page only once, starting a whole new train of thought.
At Overture, some words showed multiple times the number of searches in November than they usually do, and there was a windfall in logs that'll last through a few seasons. It's especially helpful for anything that could be popular as a gift item. Some don't know exactly what they're looking for, they'll search for "gifts for men" - good for Christmas, Valentines Day, Father's Day, graduations.
>switched to the alternative phrase
With one phrase, a high ranking was totally useless - nothing EVER came from it, even though it generally shows about 350 Overture searches. It jumped to 562 in November - still nothing, but a similar phrase with about 530 started to generate consistently enough so that minor change is in order. Maybe not for all year, but for sure worth it on a seasonal basis.