I think my G10 is one of the worst example how gray those blacks eventually gets.
I have european version TX-P42G10. I noticed this change immediately because I owned CRT TV before and always enjoyed my movies in dimmed lightning or completely dark. After awhile (500 hours max and two months) the glorious blacks became a light(er) gray. But to me this set as brand new, is a dream machine.
I posted this because no-one cannot deny it anymore after seeing those pictures. The pictures show one of the cheapest (and worst) 24" 1920/1200 LCD monitors in the market today; BenQ 2400WD. It's 2-3 years old and uses cheap TN panel and costs about 199 euros/dollars or even less. It's black level is mediocre at best. I think some might say it doesn't have blacks at all, only various shades of gray. It's gamma is somewhere around 1.4 so there are no shadow details whatsoever. Everything is washed out which is common in cheap TN displays, I've learned.
Both sets are powered on (as their lights indicates). Pictures are taken in a pitch black room with ISO setting at AUTO and ISO200 to compensate the quality of my camera. So there are lots of graininess in those photos but anyone can see the difference. Actually, ISO200 looks very much like in real life. All lights on my (AV-system) are covered with black tape except power lights.
Settings for G10:
brightness (from -30 to +30) = -30
contrast (from 0 to 60) = 0
gamma (from 2.0 to 2.5) = 2.5 (highest/darkest setting for EU model)
with these settings the screen is set as dark as possible and is unwatchable.
settings for G2400:
Brightness 50 (scale 0-100)
Contrast 49 (scale 0-100)
theres no backlight setting in this poor monitor. With these settings picture is actually too bright for pitch black room.
Lights off and camera set to auto
Picture is too dark because that BenQ doesn't have nowhere near that kind of black level.
Lights OFF and ISO setting at 200. In this photo, black levels looks very much like in real life.
I think this is a bullet-proof method to see my G10 has mediocre black level (at best). At least when compared to cheapest LCD display I found couple of years ago.
ps. I do not know much about technology or so, but IIRC real contrast ratio of that BenQ is about 400:1. How my G10 can possibly has any better contrast with this kind of black level, because both has same kind of brightness to my eyes (even when contrast set to max).
...and yes, I've used break-in slides. And yes, this "change" happened over a night (or two) on July. I bought this set on May. I haven't done anything about it because I'm lazy and thought it's just my typical luck. Still I'm not happy to hear I'm not alone with this. I'm coming from Sony Trinitron CRT and always enjoyed watching movies in dark or pitch black room. It's easy here in Finland because in winter there's no sunlight after 4:00pm. G12 Panasonic were best and only choice for me because of price and its black level.
NOTE: When comparing those photos you have to use calibrated monitor. Gamma must be set near 2.2! Using QuickGamma or similar program is good way get correct gamma to your PC display. Sorry my awkward english.