I personally never used the noob-tube on COD4, the maps were just too small, and the firing arc too eratic for my liking. I've notoced on MW2 that the firing arc is now more stable, but the rounds do less damage than those on COD4.
I personally love using the 'noob-tube' in MW2, because it is an esential tool for some game modes, particularly domination and headquarters. If i spot a bunch of guys taking a point, it is safer, easier, and entirely logical to use the weapon that does the most damage, if that so happens to be the 'forty' you have on your rifle, then I really don't see a problem. I don't just use the 'forty' for killing either, it is also a superb surpression weapon, that, if used correctly can slow or even stop enemeis advancing on your position. If you hate noob-tubers, then you will hate my scavenger M4/203/thumper setup!
I'm starting to get a little annoyed with the playlist for Domination. At present it is weighted towards the smaller or very large maps. Over the last week, I have played maybe 20 hours on domination, but I have only played on Terminal, which is my favourite map, maybe 5 or 6 times. In one 5 hour session, it only appeared once! I'm more likely to play on Estate, Derail, Wasteland, and Scrapyard comes up far, far too fequently for my liking.
One last thing. Has anyone noticed the secret challenges? I've had three pop up that are not listed in the barracks, or at least I could not spot them. I forget what two of them were, but I do remember one. Has anyone completed the 'Renaisance Man' challenge? To complete it, you have to kill three people with three different weapons in one life. The reason I think that it was a secret challenge, was because I completed it at around level 20, on my first prestige. Looking in the barracks, there was no challenge that was named that, and at the level I was at.