I'm using a Logitech G15 keyboard with display. Most of times i monitor on this display the CPU and RAM bar usage in realtime.
Running a Q6600 CPU with 4 cores, the CPU bar is sliced into 4 bars and i can tell anytime, how much percentage each core gets used.

When rendering an image, my Vue 6.5 Infinite (64bit installation) shows the use of each core with full 100%.
The renderspeeds using all 4 cores give me a good render time advantage compared to my 2Core AMD CPU before this one ...
All of my images done in the last 3 month are rendered in 2000x1600 size - and just about all of them took no longer than 2 hours - most of them were calculated in about 30 minutes.
Sure always depending on the settings and detail of a scene, logical.
But still i'm very satisfied with Vue and multicore usage.

My rendertimes are mostly shorter, too, because, for instance, instead of using the radiosity setting of a chosen atmosphere, i'll try to simulate the look and feel of the radiosity scene look by switching to global ambience and play with the light strength and light balance sliders - i can get it really close looking to radiosity - not for all sceneries, but for a lot of them ...