That's a feature that'll be out in 6.4 which will be in full use in a few weeks. The "other board" you refer to often runs beta versions and you can see the results in some of the bugs that are apparent.

There are some new features coming out in the new one that I really want to incorporate into the new version of the site, but I'll wait 'til they're fully ready.

Keep in mind that the folders on the left of the topic list effectively do the same thing. They are yellow if there are new posts since your last visit .. white if not

Thanks for the input, we're always trying to improve constantly!