If you want to see how your site is doing compared to the competition, then the new Google Trends for Websites is yet another option to conduct your research. Following the lead of sites like Compete.com and Alexa, Google Trends for Websites allows you to see a graph of traffic to the sites you designate.
But Google Trends for Websites is only adding to the confusion caused by Compete and Alexa. I used all three to compare SearchEngineWatch.com, SearchEngineLand.com, and SEOmoz.org, three of the leading search blogs. I got three very different graphs. Check out these screenshots.
With all three, there are definite seasonal dips. But these graphs may speak more to the popularity of Google, Alexa and Compete than they do of the websites you may search. Alexa makes the sites look like they've seen traffic decline, and Compete makes the sites look like the traffic has increased, beginning with a big jump last June. Incidentally, almost any site related to internet marketing seems to have a big jump last June on Compete, which was discussed at search marketing conferences and made known to a wider audience.
Furthermore, Google Trends for Websites does not offer numerical values to give you a ballpark figure of how a site is performing. Alexa and Compete do. Still, Google Trends will likely become the most authoritative source for comparison data since Google has access to far more data than Compete or Alexa.