The Player's Handbook at page 160 says, "Even if a cleric is neutral, channeling positive energy is a good act and channeling negative energy is evil." And the spell Curse Water, which imbues water with negative energy, has the [Evil] descriptor (PHB, page 216). The Desecrate spell similarly has the [Evil] descriptor (PHB, page 218).
However, there are spells that utilize negative energy but do not have the [Evil] descriptor. Examples include Enervation (PHB, page 226), Harm (PHB, page 239), the Inflict Wounds spells, and Touch of Fatigue (PHB, page 294).
Also, Manual of the Planes does NOT describe the Negative Energy Plane as evil (page 80), while it of course DOES describe the Nine Hells as evil (page 115).
So basically, would using this sword make my paladin fall? D:
*crawls under a table, afraid of an impending flame war*