Seeing a new message in our hipchat account tonight: "You've reached the end of your viewable chat history. Switch to <a href="https://www.hipchat.com/upgrade">HipChat Plus</a> for unlimited access."
And the /upgrade page refers to "Unlimited file retention" and "Unlimited chat history" as perks for upgrading. Looks like there are now some pretty compelling reasons to upgrade, even for those of us with less than 5 users.