Robert Riemann writes about an awesome workflow for pastebin using Klipper. Very cool indeed.
Here's another awesome pastebin workflow: add the Pastebin Plasma widget (which is likely to get renamed to something like "Share It" in 4.5) and drag things to it: text, images, even files! You can also just middle click on it to paste the currently selected text. It then sends it to a pastebin on the Internet and when it's done it offers a nice little notification with the URL in it and can even pop the url into the clipboard for you.
Clicking on the widget opens the last pastebin URL in a web browser window and right clicking gives you a history (in addition to the usual configuration, etc.)
There is some documentation about this very cool Plasma widget on Userbase and someone even uploaded a screencast to Youtube showing it in action.
Update: since it was a 30 second change, I made it so that when you trigger the pastebin wiget with a keyboard shortcut, it pastes whatever is on the clipboard. Fun.