Not be to annoying, but won't the most replied to threads often be those that are on the more "fun" and off-freelance-topic topics? Not necessarily always, but they tend to be the ones that get lots of replies.

How about having the admin choose topics to highlight, of only choose topics from certain forums to prevent the problem I identified above.

Current Topics which are highlighted:
===============================
[Mini Competition] Can you guess the number?

Design for retro gaming forum. Only PSD needed.

The Pope

What % of your gmail storage are you currently using?
=================================

Only one of those might really be worth highlighting really, if any.