This is possibly gonna be the shortest blog post I will ever do, but possibly one of the most useful tit-bits I have found in the Sitecore CMS. Ever wanted to force a user to select a datasource that is relative to the item its being used on ? I have LOADS of times, and after a bit of digging I found this:
Simply setting the Datasource Location to ./ (and I believe any relative path) for your renderings / sublayouts allows just this!
Every day is a (Sitecore) school day !! 😀