Pastie does. So does any advertiser who was on the page as you were pasting in that text. So does newrelic (who is dynamically loading arbitrary javascript on the load of the page).

Also, pastes are not done via ssl connections, so anybody between you and pastie knows what's in that paste, and what IP created it.

Depending on how you send that link, that messaging provider knows (for example sending it via Skype, Microsoft knows).

And thence does anybody with the legal capability of subponeaing data from any of those services.

How can the receiving party know the pastie URL?

If the sender can edit a previous paste, they can agree on a URL, but I didn't see how to do that.

If you wrote and posted it from inside Lebanon, then Hezbollah would know. Nationstate adversaries are very powerful beasts.