Well, "V for Vendetta" actually ended up OK - its dark scenes still retained enough bright material to prevent any auto-dimming (that I saw).
"Pitch Black", however, was a different story. At about the 1 hour mark, when the 'night' begins, auto-dim occurs regularly. I'd say 6-8 times during the rest of the movie. While that's still below some of the disturbing numbers posted by others during other movies, it was still disruptive and wholly unnecessary.
It is sad that it cannot be addressed by a firmware update, since I'm sure that one of Sony's programmers could add the option to the menu during a smoke break. But since its probably an energy-saving feature, I doubt that they'll touch it. I think that this excerpt from Wikipedia on "Energy Star" explains why auto-dim might have gotten more aggressive on this year's model:
ENERGY STAR qualified televisions use 30% less energy than average. In November 2008, television specifications will be improved to limit on-mode power use, in addition to standby power which is limited by the current specifications. A wider range of ENERGY STAR qualified televisions will be available. Other qualified home electronics include cordless phones, battery chargers, VCRs and external power adapters, most of which use 90% less energy.
But maybe it's not part of the 'energy star' qualification, since I fail to see how a power-guzzling TV can save a significant amount of electricity by auto-dimming like this. I guess I'll just have to hope...