Black SS is one part of the problem, the other is screen size: 
  
http://img830.imageshack.us/img830/3514/pbsslimations.jpg 
  
With the default pbss settings, what you see inside the green square is  what would be on the pbss. Can't see any larger because of the ~81000  pixel limit. Using SS rates > 1 will show more but the quality is  limited. 
  
Here is the kicker, the typical PBSS file size is about 100-300kb for a  320x240 image. X-Ray takes a full screen ss with a file size of  
  
http://img41.imageshack.us/img41/4166/0018399756.jpg