First Wort Hopping is different from mash hopping.. there's probably a better term for that though I forget what it is.
In what little I've read about it (and I can't stress that enough) the results seem to be pretty lackluster.
If you add hops to the mash then at best you receive flavor and aroma from them but I expect, and others generally seem to agree, that whatever oils (flavor) you get will quickly be cooked off during the boil.
As for FWH, the expectation is, again, that you'll get some additional aroma or flavor but, again, the oils would be quickly cooked off during the boil and little if any aroma would remain. The upside of FWH over mash hopping is that whatever happens or doesn't happen with the aromatic oils the hops at least are present in the kettle (and not in the mash tun) so you will definitely get a bittering effect, if nothing else, from them. If you feel like experimenting with it go ahead, I don't think it could hurt anything.. I just don't think it'll help. If you want hop flavor then you need to add flavoring hops toward or at the end of the boil not before it begins... of course, dry hopping is another option.
edit: here's a good, recent thread about it with some opinions from a few of the more experience brewers: