While auto-attacks will go off between "chain casted" CAs they will not go off as quickly as they were supposed to. Since a majority of our damage comes from ranged auto-attack this will have the effect of reducing our overall DPS. However you will probably not see this unless the fight lasts for 30 seconds or more, i.e. fighting a non-trivial heroic mob while in a group.
Here is how it works. You start off with a ranged CA. As soon as the CA goes off, ranged auto attack is turned on and a ranged auto attack goes off. The auto attack timer is then set based on the delay of your bow and any buffs/effects (i.e. haste, attack speed, etc) that affect it. Let us say for example that it is normaly 6 seconds but because of my buffs/effects it is 4 seconds. You start "chain casting" CAs. If one of these CAs is in the middle of casting when 4 seconds is up the auto attack will be delayed until after the CA finishes casting and goes off, then the auto attack will go off and the timer will be reset.
So what this really means is that unless I time my CAs to go off between my auto attacks I will loose some of the benifits that I might have gained by improving the delay of my bow. I just made that +1 attack speed bonus on that new set of gloves I got irrelivent. Or worse I have made some part of that Haste 26% cloak I just bought irrelivent.
Now is this going to matter in those fights vs solo mobs that take 10-15 seconds, not really. Is this going to matter in the 50+ fights that take 30 sec or more during a "instance run", you bet.
Hope this helps,