Benjamin, it's important to check every settings in your sources too. If everything is set correctly (i.e. black level must be in the 16-235 range, often called "limited" or "light"), you can try adjusting the gamma setting, which will reveal more or less shadow details, even if at the expense of overall perceived depth. I also own the 42ut50e european, and I find the default brightness setting with 2.4 gamma to be perfect for blu-rays and for videogames using PS3 as the source (i reccomend again the limited setting for black level), but if you find to lose too much detail, then keep gamma at the default 2.2 value. Also keep in mind different sources such as tv content may need different tweaking.
As for your question about black level, this is actuallt the best you can espect today from any tv on the market. Yes, a full black screen actually still appears (dark) grey in a pitch black room, but non one stares at a no signal screen for his own enjoyment, I think
. An almost
black screen but with some picture on it will already give much more perception of black. All in all, it 's still miles better than ANY lcd on the market; if you ever owned a lcd bigger than 32" you would know for sure that a black screen in the darkness not only would look a way lighter grey than your plasma, but also would be affected by horrible unevenes and white patches and if you like dark movies you definitely don't want this. I understand many people could have even too high expectations after hearing of "inky blacks" and so on, but trust me you can't get any better than this, at least until oleds are deployed.
The St50, performs identical to the ut50 in a dark room, could be a bit better in a (very) bright enviroment but delivering a slightly duller picture imho due to its louvre filter. If you are used to watch your tv in the dark, I think you made the right choice for the ut50.
Here are my settings for the euro model, could they be useful to anyone:
Mode: True Cinema
Colour: default or -1
Sharpness: 0 for 1080p, 1 or 2 for 720p, 2 or 3 for 480/576i-p
All other things: Off
Just for curiosity, which TV do you come from, Benjamin?