While I'm grateful for them hosting my images, I finally got an answer about their plus account & advertising. Basically, if the person visiting is not logged in to a plus/pro account then they will see adverts, and since the major reason for me to pay for an account was to prevent that happening then it's a loser for me.
I looked briefly at smugmug, but it was pay-only, and I'm not interested in trying it that way. 500px is image olympics and flickr are doing some odd things with their accounts/site (according to some flickr pro users I know). We'll have to wait & see.