I read an article about this last week. Here is what I took from it:
"The amount to hops to use varies. Most sources recommend using 30% of the overall hop schedule and moving it to FWH. Other sources recommend taking aromatic hops from the end of the boil and moving it forward to use as FWH. I have even experimented on my Wit beer with using FWH exclusively and had good results. My limited experience indicates that if you are looking for a smooth pilsner style hoppiness, moving a portion (30%) of the finishing hops forward is appropriate. If you want the hops to blend into the background of the beer for relatively low hop rates, you can consider moving a larger portion of your hop schedule forward. FWH in general will produce a more complex, blended hop flavor."
http://beersmith.com/blog/2008/03/17/th ... echniques/
I am thinking of trying this on my next batch. Adding my aromatic hops from the end and moving it forward. I suppose this is fine for a more aggressively hopped beer, but with a Porter I wonder if this would have the same effect.