I've been nailed a few times Cannon Striking on to Hakan's greasy stomach, but I haven't tried using Cammy's CQC in combat. Do you know if CQC works on any physical attack or are some (like Ultras or armor breakers) able to break through?

Haven't had a real chance to test this in detail, but I did run into some awesome Cammy cosplay. Hopefully I'll have more time to do this over the weekend.

Using Cammy U2 takes excellent reactions to use effectively. Unlike Hakan's U2, Cammy's must intercept a non armorbreaking move in order to land.

Counter ultras can be tricky as you have to be smart on when to use them or else you be punished bad. Fei Long has a counter U2 and if you watched the TNT stream, you saw someone got completely dominated by using it bad (Fei Long players used it and the deejay player merely took his time and ultra'd him in return).

Yeah, both Cammy and Fei Long's are extremely difficult to use, so much so that I don't know exactly WHEN one should use it. 
Hakan's, however, is extremely useful.  Not only does it stop all jump-in attempts, but it can intercept moves like the various DP's, Juri's Dive Kick, Adon's Jaguar Tooth, and even many Ultras (I personally took out an Adon's Ultra with Hakan's Oil Combination).

" Haven't had a real chance to test this in detail, but I did run into some awesome Cammy cosplay. Hopefully I'll have more time to do this over the weekend. "

Hakan's Ultra II is GODLIKE, Cammy's Ultra II is GARBAGE. 

The reversal Ultra (Fei Long/Cammy) seem to be more for the casual crowd of players. I can't imagian anyone using them in tornaments. On the other hand, Hakan's U2 is fantastic and shuts down alot of characters, especialy ones that really like to crossup alot and attack you from the air (Cammy has to be really careful cannon spiking Hakan on his wakeup or they'll slip up. I guess they could bait Hakan to do it if they done an instant cannon spike at the right distance, Bison is another character that likes to crossup and do headstomp on people, again, Bison can also bait Hakan with a late Devil's reverse ect.). When Hakan's got Ultra you gotta be really careful jumping or you'll get shot out of a poopy butt.

Hakan's ultra 2 also works on vega's wall jumps, it works on all of them but it is guaranteed to hit on jump then fly horizontal move.  It seems like it works no matter what height vega moves across the screen at.

Hakan's Ultra II is amazing. Observe.
 
 

Does Cammy and Feilong's Ultra 2 do more damage compared to their Ultra 1 just so you can say using such a difficult Ultra is worth it when it connects? 
 
I used Feilong's Ultra 2 a couple of times, and with those few times, I failed miserably using his Ultra 2... T_T