This might be a little dated since the last post was Aug 2010, but a couple of weeks ago I installed the Runcool hood louvers on my XJ (I don't have pictures, but if you look on page 1 at Sunburned's XJ, mine is identical and looks like we have them installed in the same place).
Anyway, my observations:
I am living in Haiti where it's pretty da#n hot and a couple of hours in traffic is the norm.
I got the medium size powder coated black ones, (not the "High Flow" model).
Pro's:
-Excellent quality (I used to be an aircraft mechanic and I would even say they were aircraft quality)
-Very good installation instructions
-Kit includes almost everything you need including rivets (and extras) and the correct size drill bit. Basically all you need to provide is the tape, cutting tool, pop rivet squeezer and maybe a Sharpie marker)
-Lowered underhood temperatures dramatically. The site quotes 47 deg drop and that's pretty ballpark for all the places in my engine bay that I measured before and after)
-They look awesome. I was a little afraid

hone:they'd look ghetto with the pop rivets, but they actually look really great.
-Water intrusion is NOT an issue. My XJ gets pressure washed every day to get the grunge off it and when I open the hood, nothing's wet
Cons:
- Although they are a class product; come on guys, they ARE overpriced by at least 30%. However since the Pro's vastly outweigh the cons
to me, I WILL install them on my 99 XJ when I get home.
PERSONAL installation suggestions:
-READ the instructions
-I found it much easier to remove the hood to do the job.
-The instructions tell you to tape the louver in place while drilling the holes, however, if you have access to a set of Cleco fasteners (1/8 inch), it will ensure the darn thing doesn't move when you're drilling once you've got a few holes drilled. By the time you get around near the end, the tape may NOT have kept the louver in place, (well enough for my taste anyways). The last thing you want is to get to the last rivet and realize that the thing has shifted a little with each hole you drilled (there are a lot of holes to drill). If you DO NOT have access to Cleco's, you could drill the four corners and use small screws to keep it aligned while you finish. I don't suggest tacking it down with rivets to hold it in place because you'll want to paint over the bare metal after all the holes are drilled and before you go to final install. Having said all this, USE THE TAPE TOO in addition to whether you have Cleco's or use screws. In my opinion, there's no such thing as TOO much accuracy when drilling for the rivets.
Hope this helps.
EC