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I never thought to bring it up, but I've been doing that with Poser and other apps for a while now, although my Q9550 quad core doesn't have a problem running my browser or email while Poser is at normal priority, and nothing seems to make it really use the CPU at 100% through the entire render. It seems it always drops down to 50% then 25% halfway through.

Not any more. It will use 100% till the last bucket is filled. P7 used to do that because of the way the buckets were sequenced. Basically dividing the scene into quarters to render. P8 does it differently. When a bucket finishes the very it just grabs the next unrendered bucket. This helps complex scenes render faster. Especially if one part of the scene contains more detail than the rest of the scene.

For those of you with Poser Pro you can take the trick of lowering the process priority one step further. If you use the render queue set it's priority down. Then every render you send to queue  will be rendered as the lower priority. This allows you to work while scenes render in the background.