A nice feature missing from most Unit Frames and Casting Bars in general

[tobindax]

It is not used by many similar addons but I think it helps. A GlobalCooldown indicator on the casting line. This shows if the GCD is over for casting a new one or if it's still on GCD cooldown so the player must wait.

I discovered this myself by putting Icehud's GCD bar right above the casting bar of the player. It shows in a very nice way how the GCD is going. If the GCD is still on, no point trying to cast something.