For instance you can check number of daily unique visitors for popular websites like Twitter and Digg and additionally, you can compare them on a single chart:
Clearly you can see that Twitter is growing whereas Digg has some problems with keeping the levels.
If you check Search Volume Index then you will get the same conclusion:
On this graph you don't see actual traffic numbers ...
The numbers you see on the y-axis of the Search Volume Index aren't absolute search traffic numbers. Instead, Trends scales the first term you've entered so that its average search traffic in the chosen time period is 1.0; subsequent terms are then scaled relative to the first term. Note that all numbers are relative to total traffic.It's not my intention here to show you that Twitter is trendy, I want to give you an idea how interesting information you can find with Google Trends. You can now easily check how popular different ideas/technologies/products/politicians are. Try to see for instance how rapidly is growing number of searches for ASP.NET MVC - it's growing really fast. (Actually, thanks to an article Interest in ASP.NET MVC is raising I have learned about Google Trends)
Remember though, Google Trends will give you only estimated values, those are not accurate data:
It's important to keep in mind that all results from Trends for Websites are estimated. Moreover, the data is updated periodically, so recent changes in traffic data may not be reflected. Finally, keep in mind that Trends for Websites is a Google Labs product, so it's still in its early stages of development and may therefore contain some inaccuracies.In opinion ... even though the data are estimated and not all websites are included ... it's still an awesome tool!