Google Analytics has finally enhanced their service to include calculated metrics! For users of the free Google Analytics service you can setup 5 calculations per view and 50 for the premium service. Calculated metrics allow you to perform basic calculations using various metrics in your reports. Typically you would export the data in a csv file of create a spreadsheet to do this. Now you can create the formulas directly within a view on your account.
Analytics Pros have published an article showing 25 common uses for calculated metrics that are sure to be useful for any Google Analytics user. Click the source link below to read their article and see the examples.
Source: 25 Calculated Metrics for Google Analytics