Oh, that looks exactly like what I want! Have you just built this into your own plugin?
I tried putting your code into a page template, and then using query_posts('orderby_last_comment=1');
in a Loop, but that didn’t work. I got an unexpected $end when I opened the page.
Would I need to place the two sections of code in functions.php or somewhere other than the document I am using query_posts('orderby_last_comment=1');
?