If you are using Nikon software, or creating a JPEG or TIFF from the camera, ADL can be a good choice. I did some testing on high contrast subjects under controlled conditions. I found the curve it applied was very sophisticate and produced better results than I could with 15 minutes of editing.
If you are using other software, ADL Low has some advantages since it does not change exposure and does apply a gentle curve, but it also maintains the capability of using higher ADL settings in post.
ADL does involve additional processing. I've heard it may slightly slow down the frame rate. It also is reflected in the embedded JPEG that is used for the LCD and image previews. This can show you the potential for an image post processed with an alternate tool, but it also slightly changes the histogram and blinkies. In a similar manner, you can decrease contrast of the Picture Control setting to reduce bright areas.
Testing for ADL is pretty simple. Set up the camera on a high contrast and then take a set of images at each setting. You'll see the exposure adjustment and confirm whether or not it is working.
The dynamic range of the D300s is a little better than the D90. I've noticed that some cameras tend to have a brighter exposure because they can hold the detail in the highlights.
Nice images at the US Pro - cycling photography is a blast!