How do people pick up on trends quickly and put websites out to capture the traffic?

You may want to consider looking at the link below for keyword search terms.

Keyword Selector Tool

Try this site it allows you to look at multiple search engines and their most popular queries

What People Search For - Most Popular Keywords

Try these two sites they provide a lot of current information

Popular pages on del.icio.us
Techmeme

Thanks for the links TMZ the first one in particular was very helpful

The best thing you can do is to go online and search using the term SEO tools and you will get some sites that have hundreds of tools there are some that track traffic, search terms and other items that would be helpful to you.