Not until all mainstream programs go from 32- to 64-bit are we going to see programs make use of more than ~3.5GB RAM. Of course, the programs which are already 64-bit will already be able to take advantage of much more than 3.5GB RAM, theoretically they will take advantage of up to 128GB RAM. I'm going to guess that it will take perhaps 1-2 years, we see more 64-bit applications before then though, or some applications may take longer to migrate. Already Microsoft Office 2010 can be purchased as a 64-bit application, and most of the Adobe suite is slowly moving to 64-bit. At the moment it tends to be the higher-end programs, you know the photo editing and video editing, designing, archiving and CAD design programs that make use of 64-bit technology.
If you want to make things load faster the first place I'd start is your hard disk, you can only load as fast as you can read. An SSD would really improve load times, so if you have the money I would spend it on a 128GB or 256GB SSD (I recommend the Crucial M4, it's very stable) and then replace your hard drive with an SSD and install Windows or whatever OS you use on it. I have a 128GB Crucial M4 SSD, and even though I am running it on a SATA II connection than the SATA III it is optimised for, it's still very fast! Things load pretty much instantly. RAM doesn't tend to make things load faster, it makes rendering things faster though and if you're doing HD video editing then 8Gb RAM will do you fine. What editor do you use?
