Emerald, FadeCarbon: It depends what type of 4 gate you are talking about. If you are talking about the fastest and hardest kind of 4 gate which hits your ramp at 5:45 with 6 stalkers and 1 zealot (1 Gas and probe cut at 18 or 20). You almost have to go 1 gas 4 gate yourself to stop this, with the obvious defenders advantage. DO NOT make more than 1 sentry, as they are weak and 1-2 FF for splitting is plenty.
If you are talking about the later 2 gas 4 gate, then good forcefield to split units, good positioning off 2/3 gate robo can stop it.
On your other point Carbon, Protoss is a race that heavily rewards very precise, decisive micro decisions like FF, Storm, Blink, Army formation, etc. However, Terran's micro is far more physically intense (especially infantry) and has the highest effiency. That said, one or two good timely forcefields or gravitational beams can break everything, that is the power of Protoss.
TAEdge: Knowing when and how to 4gate to punish a greedy opponent is really important. The difference between a Master level player going 4 gate and a gold level player going 4 gate is that one knows exactly why he is doing it to counter exactly what build the enemy is doing whilst the other is just doing it blindly in hopes for a victory, with Zerg usually being the victim.
Interestingly, I find 4gating a Terran to take much more skill than 4gating a Zerg. But I'm sure you already know that ;)
Edited by nGenLight on 1/18/2011 1:09 AM PST