Are you on a mac and using the system default vim? If so, Apple cripples it to not be able to directly access the system clipboard -- use homebrew's vim or macvim instead.
I am not sure which version of vim you are on. I have been using clibpoard paste for a long time in Ubunut. Do a ":version" in vim and check if it's compiled with +clipboard. If it is, then it should work.
Also, you can have this in your vimrc:
set clipboard=unnamedplus
And then your vim copy-paste will be in sync with system clipboard(no need for +p or +y).
I just tried it, it doesn't work :( That's too bad.