As I understand it the 'forceware' drivers are updated to fix small bugs and compatibility issues that occur with new programs/software/games etc. Example of this is the antialiasing sunbloom/corona effect in SHIII - you could either have AA, or sunbloom, not both; nvidia cards could not support this particular game graphic until a later video driver was released to correct it.
I have a 6800gt and have no intention of upgrading for another year or two. One thing to bear in mind is removing your old driver completely before installing the new ones, using a program like driver cleaner (google it) to clean any remenants left behind in the registry by the standard uninstall driver action. Sometimes there are issues if you do not completely remove all of the previous forceware version before you try to install the new one.
I'm sure that's roughtly how it works, if not then somebody else will be around here to put you straight
