I agree with Llama that they are never right with the weather forecast. We had one trip that my family back in IL was convinced I was having the worst weather trip ever, raining every day (per the forecast). When in fact, it only rained 15 minutes total the entire week. That being said, although a poncho owner and have gotten miles and miles out of them, the last couple of trips I have found a lightweight rain jacket from Gander Mountain that rolls up into a tiny carrying pouch that I can attach to a beltloop. I like that a lot more, as the ponchos have a habit of blowing in the wind, and the hood always seem to be covering too much (going into my eyes) or too little, pulling back and half my head gets wet.
Regardless, go have fun in the rain. And, yes the raindrops do sting a little on BTMRR, but its something you should experience once!