To add, double-check your material Diffuse_value settings under the advance tab of your Mat Room.  Most likely those values are defaulting to 100% (1.0) as per vendor preference.  No material reflects 100% diffusely, so it is recommended to drop those values to, at least, 80% (0.8) or so, depending on the texture utilized.  This, in conjunction with lower light intensity under Gc, will render more realistic results.  David suggested 20 - 50 %, but I think that is too drastic if you are lighting exterior scenes; 75 - 80% on infinite or spot lights seem to work better for full sun.  IDL works very well in PP2010, just don't use it in combination with IBL which gets very tricky and is best to experiment with until you find the right mix.  Be aware, IDL/IBL do not provide proper specular lighting, and this may need to be added as a separate source to bring out those values from the textures, if they do exist.