Well, you can use WPF and that pretty much takes care of it from the ground up, but Win32 was never designed to do that.

My point is that the long tail of apps in the wild are going to be problematic, regardless of what new apps do.

OK, so I set my DPI to 200% to check, and I found errors in every app I tried (list below), except for Dropbox, and MonoDevelop. Mostly the errors involve not everything scaling up; certain images or pieces of text will be too small.

That said, it was all purely visual stuff, and the errors were more subtle than I was expecting, so maybe my prediction was a little strong. Though if you track off the beaten path, I'm sure it gets worse - that VB6 App you use to track warehouse supplies may be completely broken.

I tried whatever I use day to day:

Opera, Firefox, Skype, MSN, FlashDevelop, Unity, VLC, UltraEdit, Dropbox, MonoDevelop, TPCView, SmartDefrag