So I had this problem come up at a table recently. an NPC had the shield spell active, and halfway through a two hour fight with said NPC (was about a minute ingame XD) told them where the AC came from.
Now one of the players has been playing since the 70's and started quoting how the shield spell is a dependent on where the caster is facing. I looked it up and how to handle a shield spell is described under the 3.0 FAQ. I've only played 3.5 and PFRPG but it was my understanding that they stripped all of the facing rules out of the game in the 3.5 versions and assumed that the shield spell saying the shield in front of you (but not giving any mechanic to define 'in front of you' or how to get around it) was fluff.
the other reason why i feel the shield spell shouldn't have the 3.0 method of operation is that they say in the 3.0 FAQ that it operates "like a tower shield" 3.5 tower shields don't give you ac bonus' only in front of you, its a straight +4. I've scoured paizo and wotc for some type of ruling on the 3.5 shield spell but found nothing :-\