GRR is one of our family's favorite rides. There's fun, laughs, camaraderie (unless you are a family of 8 you will likely be joined by strangers), and large splashes of water.
A way to just about guarantee that you'll get soaked is to giggle at someone else who just got soaked, by the way. Insta-karma seems to live on that ride.
There are also little streams of water as you're going up the, um, up part, you know, the ratchety thing you have to go up on most rides that are up high. I *always* am hit in the face (or chest), and I *always* forget about them.
I've never even passed by the ride that I didn't see some absolutely drenched people standing nearby...it's a good warning system!
Anyway, some people on some rides on GRR don't get wet at all. Other people or the same people on other times on it get splashed, others get completely soaked. Some people get a totally wet head, others get their bottoms soaked. etc etc. The raft turns around, even on some of the downhills. If you're sitting at the "door" area you'll get water sloshing in, so your leg facing the opening can get drenched.
I once had a dry downhill moment, and then some random fluke caused a bit of water to hit something, and an arc of water came straight towards me, missed my face and went right down the torn bit of my poncho to go right in the middle of, well, my bra. COLD! Shocking! Funny as anything, too.
On our last trip, my son and husband went 5 times in a row one day (I went 4), and we all went 5 times in a row the next day. After 5 times, you're really wet.
I do generally wear a poncho. I invest in an 8 dollar Disney poncho...they are nice and thick, and they last quite awhile. I did recently have to replace mine b/c it was so ripped. Some say you can take a torn poncho and get a free replacement, but I figure that I got good service from my 8 bucks and i'm not going to work the system.
On our first trip (not going on GRR) we bought the dollar store ponchos. Nasty! They are thin and clingy, they feel like saran wrap. Not a good feeling. And we re-use those anyway, as we are recycling types...even though they are thinner, they were harder to refold and put into a bag for future use. The thick Disney ones were much easier to refold.
I haven't seen the geysers on in probably a year.

I know they were on in May '08, but we went December, I went in March, we went this May and then in late June...no geysers. Don't know what's up with that! But the geysers add an extra soaking moment, b/c they are incredibly unpredictable. The actual water might be on a schedule, but you don't know where your raft will be when it "goes", and don't know what the water is going to do. Just when you think you're safe.....