I used to write a lot of native Windows corporate software in the 90's and 2000's and my standard login window was a floating draggable oval. Nothing else was oddly shaped but I did get a lot of comments on the oval login windows. It was a bit about being unique, marking my "style", and just because I could. I will add though in the 90's it did make me nuts when entire applications were wildly shaped and you had to figure out how to use them.

Editing this to add: I really miss that level of coding and working with Win32. I get that the world has moved on and HTML or some runtime flavour of it has taken over but I too lament the los of true control I once had. I hate that my stack can be broken because some runtime was updated out of my control or the crazy load times of simple projects. I know many today would say it was messy and problematic (and it could be) but it's definitely a lost art form.