When we undertook the major forum upgrade on Lustria-Online the private messages took two major leaps forward. First, members were not limited to a maximum of 10(or was it 20?) stored messages and mods were not limited to 100. I don't know what the new limit on stored private messages is but no one has come close to hitting it yet. Second, replies got folded into the original message rather than becoming a new stand alone. Hence why they were called conversations. Now we have a new upgrade that 99% of Lustria-Online probably didn't ask for. But I asked for it and @Red Devil managed to acquire what I asked for phenomenally quickly. Now you can make subfolders to store old conversations. I have a folder for moderator questions, finished story contests, ongoing contests, Index submissions, friendly chat, writing discussions. The option is there if you want it, but mostly it seems to be in place to make Scalenex and the other moderators happy.
It's not just for moderators. Thanks to this handy organizational tool, I can properly categorize all three of my archived private messages. Maybe @spawning of Bob or @n810 get enough private messages for this to matter.