Sawyer - are you you sure that you got damage reduction for the whole duration of the DR? It's absolutely not what happened in my experience... Yes, there's certain "window" when you're immune to damage but it lasts perhaps half a second - not the full 8 seconds. Also - backstabs by a spy actually reduced me to half my life...
In my opinion the DR is simply better for n00b Spies. I also agree that it makes disguises work again - kind of. You are still being spy-checked but can now turn it into to your advantage. Pyros are still your demise most of the time but with the DR the chance that you die from "after burn" is much smaller since you can extinguish the flames yourself.
Skilled spies rely more on their cloak than their disguises and that's where the regular cloak has an advantage over the DR. If you know precisely how to move around the map and when to cloak or uncloak because you are in "blind spots" the DR might not be for you since it will impede your skill. Yes, it doesn't activate instantly but usually, if you're a skilled spy, there's nobody to look for you since you killed them all. :-D
So far I heard many people express their love for the DR but at the same time players who I know as good spies don't actually use it although they have found it...
In my experience, the eight seconds of invisibility usually suffice. A good example would be 2Fort. The enemy team had sentries on the lower level of the stage room. I just ran into the enemy's fire, thus triggered my DR, and there was enough time to make it to the top of the spiral.
I should mention that I don't think I am totally right and the DR doesn't have any downsides. It's just that before the update I died a lot as a spy and was happy when I could get at least one backstab. Now, with the DR, I get to make a lot of more backstabs and I don't think that my skill suddenly increased
Yeah - but I think this actually is map dependent. We all know how difficult it is to sneak by as a spy on 2fort thanks to its awful chokepoint design and in this case the DR helps. However, on more open maps it's practically useless. E.g. I tried it out on Badlands and virtually every time my cloak triggered because I got shot I was in a place where I wasn't near any "stabbable" enemy or even a good hiding place and hence could only run back and try again.
I think my analysis of the DR is accurate in that it's designed for "chokepoint 0wn4g3" while the usual cloak is much more subtle and works best when you are deep behind enemy lines or absolutely sure that the enemy won't be able to pursue you. The hard part is getting behind enemy lines with the regular cloak. ^^
By the way - I found that the Dead Ringer is an awesome part of "psychological warfare" where you might leave the enemy at a disadvantage even though you actually died.
E.g. today I was killed twice by players who knew that I have a Dead Ringer. They asked me at the next opportunity if they REALLY killed me the previous time since they went looking for a spy for the next 30 seconds. ;-)