About the Skill:

Arms Lore is a skill used in the crafting of certain items and to identify the condition of a weapon. However as to the latter use, any character can determine the same information via the item's tooltip.

Professional Title: Warrior
Maximum Skill Possible: 100
NPC Trainers: Armorer, Blacksmith, Blacksmith Guildmaster, Weaponsmith, Weapons Trainer, Fighter, Warrior, Mercenary, Paladin, Merchant Guildmaster, and Warrior Guildmaster.
Arms Lore was no longer considered a "Useless" skill as of Publish 44 which was released in April of 2007. It now compliments the crafting of armor and weapons in the following ways.

Gives a +1% Damage Increase bonus to all exceptionally crafted weapons for every 20 skill points (up to +5% at Grandmaster), (1% for every 12.5 points ArmsLore, up to +8% at Grandmaster on Shard Siege Perilous).
Gives +1% in a random resistance on exceptionally crafted armor for every 20 skill points (up to +5% at Grandmaster), (1% for every 12.5 points of ArmsLore, up to +8% at Grandmaster on Shard Siege Perilous).
these bonuses apply to all crafted weapons (metal or wood) and armors (leather, metal, and wood);
these bonuses stack, or combine, with properties imparted by Runic Tools.