Al: I agree it can be a useful plot shortcut, but look at its severe limitations:
1) Let's say you play it safe and contact a Demideity. To begin with, that's a DC 10 _intelligence check_. Not a will save, an intelligence check. So, let's say you are a smarty and have a +6 intelligence bonus. That's a 15% chance that you are going to twiddling your toes and smiling at the daisies for two weeks.
Next, lets say you have a burning question to ask. There is only a 50% chance that the demideity knows the answer, and a 30% chance he gives you the wrong answer. So there is a 42% chance you get the information you need. On the other hand, there is a 15% chance you're insane (with no answers), a 17% chance that you have no answer, and a 26% chance that you now have the wrong information and don't know it.
You can keep asking questions, say 6 at 12th level, but you will only get on average 3 good one word answers (and 2 misleading ones).
2) Let's say you get tired of that and deside to contact a greater deity. The greater deity has only a 10% chance of being misleading, but since you have a 45% chance of taking a long vaction (DC 16 intelligence check), you aren't getting much better results. You get the information you need 49% of the time, you are insane 45% of the time (with no answer), 1% of the time you get nothing, and 6% of the time you get a misleading answer.
One thing that I wish showed up in the latest incarnation of the FAQ is whether or not the effective ability decrease is intended to be curable by a Heal spell or the like. One would like to assume that it is (otherwise this spell simply isn't going to be used), but I'm not entirely sure because the wording is quite vague.