If I were wearing full plate (which has a max dex bonus of +1), but my dexterity was 16 (a bonus of +3), does that affect my BAB with ranged weapons, or just everything else dex-related? Thanks.
The Armor Check Penalty affects your dex-based skills; and if you don't have Heavy Armor proficiency, it also affects your attack rolls (both ranged and melee).
If you do have the Heavy Armor proficiency, your attack rolls are unaffected.
Armor (with the possible exception of a Tower Shield) has no effect on Reflex Saves.
Sorry, I was not completely accurate. There are certain skills - often marked with a * on a character sheet, or listed in the PHB - which are affected by the Armor Check Penalty.
Jump, Climb, Hide, Move Silently, and others.
Some are Str-based, some are Dex-based.
Swim is a special case, affected by the weight you are carrying (including the weight of your armor), rather than the ACP.
You can also use a Mithril one, that allow +3 of dex to Ac, its is expensive, but its a beautiful armor. Can you imagine a full plate made in mithril? The Dwarves love this kind of armor.