It seems irdeggman has the same reading of the rule as I do. Attacks are made against 1 target unless specified before rolling. I have no problem with rolling at the same time to save time but you need to inform before hand what you intend to do with your attacks.
Yeah but the problem that can arrise when attempting such a "time saving" action is that you now have problems with changing your target - which by the RAW you specifically can do for subsequent attacks.
Or even switching from a full attack to a standard attack if the first attack felled your opponent (or even had no effect) - again the RAW specifically allows you do to this.
All of the potential "issues" with making multiple dice rolls at the same time need to be thought out (and probabaly explained) before doing such a thing or else things can get real "messy".