Hot Trends aren’t the search terms people look for most often — those are pretty predictable, like [weather] or [games] or perhaps [myspace]. Yes, [sex] too. Instead, the Hot Trends algorithm analyzes millions of searches to find those that are deviating the most relative to their past traffic. And the outcome is the Hot Trends list.
This makes Hot Trends more than just a search term popularity ranking web site. The analysis used are more leveraged towards seasonal popularity and offsetting them from consistently popular search queries. Pretty smart analysis… not that I expect any less from el-Goog.