You can see how popular a search term is on Google, and it’s updated every 48 hours so you can also get up to the minute data, or view up to 4 years of historical data.
It also has a neat feature which allows you to compare multiple search terms, particularly useful for vanity checks on how often people are searching for your brands (or your competitors).

Here’s an example which should help to illustrate how it works:

clinton

obama

Click here to visit Google trends
Now, keep in mind, the figures are a little rubbery (there isn’t even a precise scale on number of searches) but it really gives a nice overview.