Video cards have an Idle clock, a 2D clock, and a 3D clock. My GT 430's Core Idle clock(when I'm at the desktop browsing the web) is 50 MHz, my 2D clock is 405 MHz, and my 3D clock is 825 MHz, which only kicks in when I'm gaming/video editing, etc. I'm not at my desktop right now so I can't give you the clocks of my memory and nVidia shader, but I do remember they varied along with the Core clock.
624 MB of memory? Really? Check in GPU-Z and see what it reports...