Don't feel too noobish. I have been playing wizards for almost a year now and didn't figure this out right away. (And, I still may not have the whole story straight.)
Combat Casting is described in-game in such a way that many players don't realize exactly what it means because the description mentions the combat mode so casually. I.E., one may not realize that "when casting defensively within four meters of an enemy" doesn't just mean casting while trying not to get hit, but actually casting while in the specific 'defensive casting' combat mode. Since defensive casting makes casting every spell as hard as if the caster got hit for 5 hp during casting, it is a crummy mode for lower-level casters whose concentration skill isn't likely to be very good, (And, it's arguable whether the feat is that great at any point.)
Unfortunately, Combat Casting, while nearly useless on its own, is required for Improved Combat Casting, which is largely useless, too, but also very convenient. By the time a caster can take ICC, his concentration (likely 24 + constitution bonus + focus feats + magic items) is basically high enough that he should just use the defensive casting mode all the time in close combat, since it costs noting and, with an adjusted concentration skill of 27, a caster will always make his defensive casting concentration check. So, why bother with ICC? Because it's annoying to keeping flipping on the combat mode after every movement, particularly when the player is to trying figure out which of the forty spells that he has available will be useful against whatever blurry maelstrom of sticky death is speeding his way. He would benefit more from an "Automatic Defensive Casting" feat. It's a shame to waste two feats just to avoid having to scramble around pressing keys.
(Of course, there may be a better way to enter defensive casting mode, and I would love to hear of it. But, aside from the obvious step of assigning another precious quickslot, I don't know of a way.)
BTW,
HipMaestro wrote...
edit: Incidentally, the easiest way
for a caster to avoid all attacks of opportunity is by equipping a range
weapon.
I know we're joking around here, and I know that a caster will not be tempted into
making an AoO if he has a ranged weapon equipped. But, just to make sure no one new to casting characters is led astray, the discussion, at least regarding the casting feats, was about AoOs that others gain
against the caster, triggered by his casting a spell. Equipping a ranged weapon will not help the caster avoid others' AoOs.
