Animals, Gary says, will always be able to sense "ulterior motives," when subject to this spell. Because Gary's players were apparently shameless enough to run Druids that would take advantage of animals.
Charm Person or Mammal
Gary gives some nice guidelines concerning how to adjudicate this spell; namely, this spell only changes the subject's basic orientation towards the caster into one of friendship and acceptance. This is not, as Gary says, "enslave person or mammal," nor does the subject's attitude towards the caster's associates change significantly (though presumably the caster's associates will not be attacked except in self-defense or if provoked).
Hilariously, Gary needs to point out that this spell will not create water in any part of any living thing. Because one of his players clearly tried to do that, most likely with the aim of making said creature explode.
Held or Wizard Locked doors can only be affected with this spell if the Druid is of higher level than the Magic-User who held or locked the door, and then only with a 20% chance for every level the Druid is higher than the Magic-User.
This spell is presumably useless within, say, the confines of a dungeon, but, conveniently, a Druid may call half-strength lightening out of a whirlwind created by a djinn or air elemental.
Call Woodland Being
An interesting list of possible beings that could respond: brownies, centaurs, dryads, pixies, satyrs, sprites, a treant and a unicorn. I almost expected a dragon, a la the Ranger follower charts.
The reverse of this spell can be used to quench, and strip of its magical properties (!), a flaming sword. On the one hand, this is a seventh level spell; on the other, that seems like an awfully easy way to disenchant a magic sword.