There are numerous obstacles to getting a good photo of the arches. The first being that they are so huge it's hard to frame them without obscuring them with trees. The next problem is trying to not blow out or underexpose any part of the image.
I really wish that I could get to shoot at dawn or dusk and it would help eliminate that problem. But for some reason my schedule always gets me to my location at about the worst time of day, when the sun is directly overhead. Furthermore, it seems that I'm always shooting directly into the sun. One day I'll learn that sleeping in never facilitates the best photographs.
As for not over or under-exposing the shots, I was only marginally successful in that. By taking 5 bracketed photos (+4/-4 ev) I was able to get a much wider spectrum of light in each photo.
The full set of photos can be seen here: http://www.flickr.com/photos/chucksutherland/sets/72157625137407632/with/5082358489/