Google announced a new service today called Hot Trends...which is really just hot flashes of the day...not really trends. They list the top 100 search terms of the day measured by their deviation from the norm. So, terms like sex, MySpace, etc don't show up unless they are abnormally high that day.
What is interesting about Hot Trends is that it points out how fickle search users are. There are no trends...they search for everything. My guess is that only a handful of the hot search terms today will show up on the Hot Trends list tomorrow.
However, that doesn't mean there isn't a way to optimize the search index for popular search terms. There is indeed a way to do that, and Google Zeitgeist provides a view into what terms should be optimized. Analyzing the Zeitgeist changes you can identify trends and shifts in popularity.
Web search is a tough business - After 10 years and billions of dollars spent the web search scorecard reads; Google 70%, Yahoo 10%, MSN Live 4%, AOL 2%, Ask 1%, and everyone else less than 1%.