I replaced my OEM radio on my 17 SL with a JVC head unit. I now have 7" touch screen, plus all the other bells & whistles. I love it, but like @chavey2 said...it is not waterproof. If this is of concern to you then I would highly recommed this Sony unit. It is not waterproof, but I watched a review with it being sprayed with water and it looked like it had no effect on it's operation.
For me, being waterproof wasn't a huge factor. I did make a plexiglass cover to help if I happen to get stuck in the rain.
Here is my setup....Stereo Setup