Reflecting Pools are very useful features if you want to get to an instance quickly. However, since Moria, they have been changed.
Where you used to be able to enter an instance if someone in your group was already in and do your quest, they are now only to be used for helping someone do a quest you've already done. If you enter an instance through the pool, the quests will not complete for you and GMs will not do anything about it, because it works as intended. Or at least, this is what we in Europe hear from GMs.
Bas Scholts / Rhyaehar