This is sad but it is true. i have submited my wallet in about 20 giveaways and got coins from 5 of them...
I did the same thing a while ago, I then spent a couple of hours compiling a list of where i had signed up and waited to see if they coins paid out.
I found the same results as you, it was maybe 5% of the faucets i signed up too actually paid out within 2 hours. I went back at the required times and the ones that worked ended up being out of coins.
I have noticed various random tiny amounts of coins appearing in my cryptsy account. So it could be that the give away you signed up to has some additional requirements (several i saw needed at least 10 people to sign up before it paid out.)
As with everything in life the best things never seem to last ^.^ (but do check back! lots of them run on donations)