Yep. There are limits to overexposure recovery using Raw, and the best application for doing that is ACR - Adobe Camera Raw (CS5 Camera Raw/Lightroom 4).
The color in a digital photo is is made by combining 3 colors red, green, and blue - RGB. So each image has those 3 RGB color channels, and how much of each channel there is can be checked by sampleing some potion of the photo. The sampeling tool can be set to sampleing pixle-by-pixel, or to sample larger square pixel arrays, up to 100x100 pixels. The sampeler displays all 3 RGBcolor channels.
The luminosity of each color channel ranges from 0 to 255. Zero means there is none of that color at that point in the photo, and 255 means there is the maximum amount of that color at that point in the photo.
When all 3 channels are
0, 0, 0 - the color is black.
255, 0, 0 would be
red.
Green would be -
0, 255,0.
Blue is -
0, 0, 255.
Yellow is 255, 255, 0. Magenta is 255, 0, 255. Cyan is 0, 255, 255.
Pure white is 255, 255, 255. When all 3 RGB color channels are maxed out at 255 there is no detail, just pure white, a condition also known as 'blown out' because there is no detail. No details can be recovered when all 3 RGB vlaues are maxed out.
If with over exposure only 1 channel is blown (maxed out) - say 255, 240, 240 - most of the detail can be recovered using judicious editing adjustments.
If 2 channels are blown - 255, 255, 240 - a little detail can usually be recovered, but not as much as when only 1 channel is blown out.
The other extreme 0,0,0 - or pure black is known as blocked, and again there is no detail.
Real World Camera Raw with Adobe Photoshop CS5
The way digital images work, we usually want as much image data as possible as close to maxed out as possible without blowing out a lot of the photo. (Known as ETTR -
Expose-To-The-Right of the histogram)
Some bright spots, called specular highlights will, by neccesity, be blown out.
http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf