I find IO to be the biggest bottleneck right now. There's no point being able to crunch through 10GB of data on your CPU in under 500ms if it still takes 30 seconds to read it from disk.
I also want to know why 3D games from 12 years ago have more responsive hardware accelerated UIs than a WinForms WebBrowser control embedded within a WinForms UserControl embedded within a WPF control, contained within a WinForms form (this is some of the internal software we use). The window takes 3 seconds to handle a resize event.
software rendering and abstractions on top of abstractions on top of abstractions?