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

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.

Quartz has a GCD module, as do AZB and Gnosis for example.. It's one of the most common modules for castbars imo because I never use it, and I've always had to shut the damn thing off :P

Ya, same way. The GCD indicator on my action bars are more than adequate for me to use.

Who uses a GCD timer anyway??? SPAM THOSE SPELLS FOR MAX DPS!!!

I used to use a GCD monitor. Back in BC, when I raided on a hunter.

Of course, I paid more attention to the Swing Timer I was using, since, well, you didn't wanna gimp yourself on DPS by spamming Steady Shot, since it pushed back autoshots...

Then Wrath came out, and that didn't happen anymore, and all the hunters rejoiced... and dropped their GCD and Swing timers. :>

I use mine occasionally (I use the addon called Castbars). Usually when several haste buffs kick in and I'm timing my Arcane Blast, watching the two latency marks that Castbars has and the GCD.

I prefer not to break my keyboard and to have mercy on my sore hands. I have a good feel for when to press the key and only hit it 2 or three times at the most.