There are several uses for the extra memory including just using the memory using a memory filesystem. I use 4GB of ram constantly and I don't do any type of heavy editing. I just use the ram however I can.
What do you mean by this? Do you mean that you manually use ram like a ram disk somehow....or are you saying that programs automatically get loaded into RAM so more RAM equals more programs that can be held in RAM? If you are speaking of the latter, let me assure you that Safari, iPhoto, Mail, iChat, Contacts, Calendar and iTunes will all comfortably sit inside 2GB of RAM without paging. This is typically what most users will have running day to day....so again I stand by the fact that most users will never really put 4GB of RAM to good use.
By the way with the faster SSD, applications seem to load fast enough that you almost don't need a huge pool of RAM.
Kan-O-Z