I was just getting ready to write a function that would append the planner annotations for all of the process-marked articles in a Gnus summary buffer to the kill-ring, so that they could be yanked as one into a buffer. I thought this would be handy for saving links to an entire e-mail thread rather than just a single message.
Turns out planner-gnus already does this. I marked all the articles in the thread, then called M-x planner-annotation-as-kill, and yanked the result onto a plan page. This produces a link titled "5 E-mails from folder nnml+~/Mail:misc". Following this opens the nnml+~/Mail:misc summary buffer and displays those 5 messages. Neat.