Well, I may as well chime in too. I have had my COBB S2 setup for about 4 months now. It is sweet with a capital S. I just got a chance to use the S2 STX map about a month ago and that is awesome. The versatility is key.
I have an UP, DP, CB, and intercooler hoses. So, I am just beyond their S2 specifications. I put my car on the dyno before I flashed my car to stage 2 and got 213/213. I then flashed my ecu on the dyno and did some more pulls. That time I got 232/233. An instant 20 whp gain, and have probably gained a little more since the ecu has had time to completely learn. For $595 I couldnt be happier.
Like others have said it is very smooth and fast. I chose Cobb, because at this point in my modding I wanted something conservative and safe, with the option of upgrading in the future. I cant wait to go to S2.5. I am hitting above Cobb's target boost, but also have the few other mods listed above, plus use 93oct.
I think this about covers it. If you have any questions feel free to ask.