Dang I left a nice message and then got an error on submit!
We use SFDC campaigns to track responses - anyone who's actually completeing a Call to Action.
But I look at Marketo to understand the finer level of detail - what subject line gets open rates, what gets email clicks, what gets form fillouts.
If you use Marketo's Program Statuses, and record the cost in Program Settings, you can really easily do a comparison of campaigns using the Program Analyzer.
Because we started using Marketo because those features were available, we adapted and made our own "system" for tracking the responses in SFDC. But now we're starting to use those features and hoping to get a bigger, and better, picture of what's working and what's not!