Make the infos like browser agent, javascriptversion, OS and additonal infos available in the results.

Some workarounds are not working with different browsers. E.g. you wonder why a hidden question was filled out with a invalid value (solution, very old browser wasn't hiding the question). If you have the additional infos at hand you can quickly pinpoint what might be the cause of that answer pattern.

The variables could also be made accessible for conditions.
But to save them into the results would be already a big help to give feedback about problems and weighting them in terms of how often they would occur in the field.

In many surveys what I needed to collect was year only or a year/month combination. Of course I could create custom combox but using a predefined question type is always easier.