There are a couple tools on the web which allow you to track your competitors click through rates.

Google AdWords Click Through Rate Tracking
The first one is a free offering from Google. Underneath the ads there is an Interest Bar which looks similar to how PageRank appears in the toolbar. This value is based upon clickthrough rates.

Some programs such as AdWords Analyzer will look at the number of advertisers for a keyword, but it does not show the click through rate. Looking at the green bars at the bottom of the AdWords ad will give you a good indication of how competitive a term is. If we search for something like "Google AdWords" you will see that most of the Google AdWords ads have a decent click through rate <--- exceptionally competitive marketplace.

Some other ads are not as well targeted and/or are poorly written. This causes a lower click through rate. You should notice different interest levels on some of the people advertising for words such as "drink wine."

Since Google AdWords factors click through rate into click price it is exceptionally important to maximize your click through rate.

Overture Competitor Detail Monitor
A company by the name of Epic Sky offers a product called "Competitor Watch." It can track the spend and bid strategy of your top competitors. It does not; however, tell you what words your competitors are running ads for if those words are not already in your inventory.

(found in Catherine Seda's new book. Search Engine Advertising : Buying Your Way to the Top to Increase Sales)