I cannot vouch for the other sites, but at Skyscanner we looked at the aggregated search history (12 million users a month) to make a best guess at the default dates to set.Interestingly the defaults we use are different for the mobile platforms. (We use our own backend technology)
Can you provide a little more detail on this? What percentage of users actually use the defaults (for both start and end date), and how many change it anyways?
Have you thought about doing some A/B testing on providing a default and not?
