The second part of the guide to ROI being posted on Google's Inside AdWords
blog covers the use of the conversion tracking code that's provided free to AdWords advertisers (who use the Standard Edition). If any form of 'action' is taken on a website, then the conversion tracking code should be used, plus if a value to the action - such as a sale, enquiry or newsletter sign-up - can be assigned, then this can be included in the code and then reported in the AdWords stats.
The value figure can either be set as a static amount for every action, or transaction, or if products or actions generate different levels of profit, then the value can be dynamically generated from each conversion. The article provides an initial overview to the process of setting up the value criteria within an AdWords account and also has links to other useful resources or guides.