Is al DLC region locked?

Hi everyone.

I don't know if anyone will have an answer to this question but it's worth a try.

Now I know that everyone got mightily p****d off with the CoD4 regional locked maps. I had to buy them twice and I still never got refunded from the UK store.

I purchased some songs off the US store for my Guitar Hero three game, and it doesn't work. There are no warnings on the store to say that these won't work. What the hell is going on with Sony.

Does anyone else have any problems with DLC?