I agree with mpaper that people will explain away a drought of 3 years, mostly because just having no rain for years at a time isn't anything new.
I think contemplative is right that turning it on and off at will is what will cause people to stop and think.
Also the revelation says that the AC and his false prophet will be able to perform miracles (albeit false miracles). It says they will call fire down from Heaven. So we have two groups of 2 calling fire down from Heaven and (presumably) both preaching in the name of Jesus. (I believe this is why the false prophet is described as having the horns of a lamb i.e. he will try to make himself sound like some kind of holy man, but his teachings will pervert people away from the teachings of Jesus).
Anyone trusting in a miracle as a sign of who to follow will almost certainly be conned into following the wrong guys. The same Jesus who said to believe him for the sake of the miracles he was doing also said that an evil generation seeks a sign.
I agree with journey41 that "Revelation" means to reveal and it always will be an unsolvable mystery until people start trying to understand it using Jesus as the cornerstone. I think that makes the most since. If it is meant to reveal Jesus (i.e. the Revelation of Jesus Christ) then it makes sense to go back to the teachings of Jesus as a comparison.
For example Rev 13 talks about a mark, initiated by the AC, without which no person on earth will be able to buy or sell. If you take the mark you will be cursed by God, but if you don't take the mark then you will be forced to find ways of surviving that does not depend on working for money.
I think, because the idea of not working to get more money sounds so wierd and extreme, most people assume it is talking about something else, but Jesus said something very similar in his sermon on the mount.
He said that we cannot work for God and money at the same time without cheating on one or the other. (matthew 6:24-34)
He said all the world runs after material things, but that we should not be like them.
He said that our job is to seek God's kingdom first and then God would take care of all the material things he knows we need.
As we start to compare the lessons in the revelation to the teachings of Jesus it becomes far less confusing or scary (although, like john eating the little book, it can be fun (sweet honey) to crack the code and put pieces together, but when we start to realize the cost of what following Jesus means in the context of the revelation (i.e. not taking the mark) most of us start to feel a bit bitter in the tummy.
BTW, at this point I'm leaving off a lot of the scripture references but if anyone wants me to quote something specific I can try to do that too. Just let me know.