I have to say that the ATCSCC is very pro-active.
Yes, terminal forecasts play a significant role in driving MIT, GS, or a GDP.
But essentially, they are very pro-active and are very skilled at what they do. But it still doesn't help when the airlines are scheduling more flights than the system can hold, hence the delays, then weather, hence the ground stops, MIT restrictions, or a ground delay program (wheels up time, pushback times, etc etc.). RVSM has helped increase system wide capacity, but you still have to compress that space down to the terminal level in the same amount of distance . . . so in reality the enroute environment can hold more, but the terminal environment is still the same sized glass it use to be, still only able to hold X amount before saturation and bursting at the waist.
In your spare time, take a look at the NAS Playbook. Each major airport (C / B Airspaces) have plays that can / will be used when needed. Pretty interesting stuff.
On the weather side of things. . . take a look at this UCAR / MetEd seminar. Takes about 30 mins or so, you can either download it to your desktop or view it online. Either way it is a gold mine of information on how weather impacts the NAS.
http://meted.ucar.edu/nas/index.htm