often I get the question how active people are and that includes how often they have responded to an offer.
First question would be: are you doing something similar and how do you do this?
At the moment I'm thinking about a.) adding database field on a lead record Offer count all time (content) Offer count quarter (content)
b.) increase the total of that lead record field by +1 using a trigger campaign every time, if someone fills out a form and if the offer type is a content piece (whitepaper, factsheet)
that brings me to the Second Question: I'm pretty sure there are better ways to do this, as we also have events and activity on other channels. So that would mean we would need additional database fields on leads like "Offer count all time (events) etc. .
You can do this, you can also try to count up SFDC Campaigns or Program Success/Memberships. But the only way to get a number fast is to do what you are planning and then have Marketo or SFDC add +1 to the field for each response.
You should only need ONE field to do this.
But if you want to break it down by quarter, maybe you need to create a custom Campaign Member record. There are some thoughts on the blogs at Perkuto, OpFocus, and full Circle CRM sites.