Lady Deluxesaid: I've never seen 'Hot topic' in these forums...
They were an old feature. Made it convenient for players to keep-up-to-date with the most active threads, instead of skimming through different threads searching for a quality thread worthy of response. Saved yourself from swimming through all the spam threads.
I'm not sure why it was taken down though. They were a great alternative to the stickies. You didn't have to wait for a J Mod to sticky your thread, just the quality of your thread would do justice. Of course, some threads tend to be slightly more controversial which attracted the wrong kind of attention.
Many other forums out there practice this, it's a life-saving feature!