Microsoft’s attempts at Fluent over the years are a striking example of why engineering and design need to work hand-in-hand.

On Windows, concepts like acrylic and mica are nice, but are terrible for performance over Remote Desktop, RDP being a core strength and differentiator of Windows (especially with the push to sell cloud-based subscriptions and thin clients).

The other thing that drove me nuts is lack of care for low-res (aka full HD) displays, where rounding and thin borders leads to visible artifacts in common controls. A designer who uses high-end mac devices will never see these things. UI/UC Design isn’t meant for museums, it needs to be built in dialog with the real world application.