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