In your case, Vram isn't really an issue.
512mb is more than efficient to do anything OSX wise, even opening a bunch of windows, as they only take just from 8-10MB
You might notice some sluggish animation when using an external monitor and having anything over 1080p. Otherwise it should be fine. Higher pixel counts benefits with more vram. Otherwise if you are using your LCD screen on the macbook pro, no worries.
The only time when one needs that much vram is pratically gaming, though OSX games should run efficientely, including normal games running in windows, I can't say much for high end games like Skyrim or Rage that uses high quality textures. The game will pause/break once in a while just to load new ones into the video memory from main ram to framebuffer. versus having it instantly. Its not annoying by any levels but you will notice the pauses. Nvidia does a great job with buffering more textures to memory than ATI, ATI cards you really do need more vram. Games like Skyrim will benefit from extra Vram, even some options i believe are turned off unless you have 512MB or more vram. Otherwise general games doesn't really matter
http://www.youtube.com/watch?v=7i0ayaPNajI This is a prime example when you are running a game that uses high quality textures and low on vram. It runs smooth framerate wise, but you can see textures popping in and out because of low vram, though there are fixes to help make it smoother.
http://www.youtube.com/watch?v=mYuB7wtqneU this is the same game running with 512mb of vram, it runs fine, but if you look very carefully there are texture popups.
though this is with games that requires high end cards because they have high quality textures. Most other normal games will run fine.
But then again, if you are really gaming, why get a macbook pro? :> Don't think about using parallel desktop too if you are going to do minor gaming, it will chew faster on vmra
As for productive applications, the only thing i can think of is when doing 3d modeling, you do need the vram as having less makes it studdering and it can be annoying in a workflow.