Magic Weapon duration is turn/level
When my bard casts this spell it has the same duration as my mage armor. I'm thinking this is hours a level, in which case it's a bug. Maby this is just for clerical Magic Weapon though? In which case this next part is irrelevent.
Quite a few quests seem to require magic weapons. It also seems that the few people with a magic weapons rock everything. In my (probally biased) opinion the spell is working fine just now. It's okay to have a spell caster make a blade magical because at low levels it's temporary (10-25 minutes) and at high levels they probally will have a magic weapon.