8 GB memory in any laptop with "Pro" written on it is laughable. Apple have always been stingy with memory, but I feel like the 8GB base memory config in the MBPs is egregious. In any of the other Apple laptop lines 8GB is an acceptable base spec, but the Pros should come with 16GB standard.
If you are doing any kind of professional/student work that includes imaging or visualizaton, GIS, rendering, video, photographic work, or advanced quantitative analysis I'd recommend 16GB (or more). For writing, basic image manipulation, simple programming and just general computing you might be completely fine with 8GB for years.
With that being said, web browsers can be horrible memory hogs, so if you either prefer having lots of tabs open at once, or do web development work, 16GB of memory may be necessary...