Updated with Numbers
Well, I started this thread and I've had my nMP for a few weeks now, so I feel compelled to give some numbers.
Again, to put things into context, the last machine I did Handbrake encodes on was a PC with an Intel 3960x Extreme 6-core running at 3.3GHz. That machine averaged about 3 hours per typical Blu Ray movie.
My nMP specs are in my sig. With this baby I'm averaging about an hour per movie encode. I'm pegging mid to high 60's in FPS and I'm using the ATV3 preset. My source is MKV rips.
Also, someone mentioned Compressor. It has its uses, but this isn't one of them, especially since as far as I can tell it cannot handle MKV containers as a source. Handbrake is still the champ for this specific purpose.