I just wanted you guys to know, that I wrote an app that allows you to create big multi monitor spanning wallpapers on the fly with live feedback.
You can check it out at www.wallsexperience.com.
I put a lot of work into supporting the Wallhaven API (IMHO the best source for wallpapers).
Even if this is my first post, please do not consider this spam. I'm a wallpaper aficionado as all of you, otherwise I would not have put that much work into the app :)