This is nice, but i think 30 is quite much. I like to download nice wallpapers to my comp, and i'm doing this from other sites too...but this 30 seems to be too much, it might make this credit system somehow useless.

My solution:
about 8 free download quota
and you will gain 1 free credit in a day, so you won't run out of credits.

hmmm....maybe my solution isn't so good...well this was just a thought.