The Flickr API allows to set two dates for each photo: the date when the photo was uploaded to Flickr (this also determines the position in the photostream) and the date the photo was taken.
http://www.flickr.com/services/api/flickr.photos.setDates.html
Please add an option (a checkbox for instance) that when chosen will set the posted date to the creation date of the photo (from EXIF).
Please note that you cannot set a date earlier than the date the Flickr account was created, so you'd have to set earlier dates to that.
This issue would help improve Flick in a way that has been subject to a lot of debate. Some people feel that photos in the photostream should be ordered in the chronological order when they were created instead of when they were posted. However, while Flickr does allow one to edit each photo individually and set the posted date, it does not offer any means to do this in bulk or an option to set photostream ordering to creation date.
Therefore I think that such a feature would be a very interesting asset for KFlickr.