It doesn't annoy me, as long as they link to a rot13 translation site.
Come to think of it, as long as they're linking, they could just have a website where it just tells you what it is. Perhaps just have it have rot13 in the URL and use that. Does anyone know a website that does that?
Sorry I'm late to the game, but yes, I happen to have made such a website.
http://www.lightning-rose.com/projects/rot13.htm
Text input is converted to raw rot13 text, raw URL, HTML URL, and UBB URL.
Here's an example of a raw URL:
http://www.lightning-rose.com/projects/rot13.htm?Yvtugavat%20Ebfr%20znqr%20guvf%21
Every time I come across one, it annoys me. I have to copy the text, open a new tab to the ROT13 site, paste the text, and click the translate button.
Compare this to something like a collapsable spoiler button-box where you press a button and it expands and expands a box with the appropriate text underneath it. Even making a [spoiler][/spoiler] tag that gave a black background and equally black text would be better than the current ROT13 solution.
Was there actually a reason for doing things this way? If so, why not just include the ROT13 translation in the javascript that'd open and close the textbox? Comments? Criticism?