This is just a little tip for anyone having trouble with the wing and a prayer Achievement.
I was playing through some L4D2 last night and noticed no matter how many times I did the wing and a prayer achievement it just wouldnt unlock for me so i just gave up and moved on. The funny thing is when I got round to installing the game on my hard drive(by this point I had played some games online and only had the last mission left to do) I went back and did it again the exact same way and bang the achievement unlocked for me.
So anyone having problems with this achievement not unlocking or any others maybe you should try installing the game on your hard drive it might work for you guys to.
P.S. Off topic Im really sad that the DLC for Dragon age has been delayed until futher notice.
