...they're actually slightly different, being nit-picky. The New Posts shows you the threads that have been added to since you were last on the board. Whereas the Today's Active Topics shows you all of the threads that have had activity in the past 24 hrs (or since midnight maybe?).
There are times when I want to re-visit a thread that was active earlier in the day, but doesn't show up in the "View New Posts" search (and I don't automatically recall which Forum it was in, or I'd just go to it). If it weren't for that, then I'd probably be happy with just the "View New Posts" option.
To me, the "Today's Active Topics" is (was?) one of the best things about this board's software, and having a TAT link on every page was extremely convenient. Navigating and keeping track of threads and thread activity is so much more simple here than say, AAJ. So... I'm hoping it comes back.
As of right now, I'm getting back to it via my browser history trail, and then refreshing the page. BTW, I think it was at the BNBB (or was it the original Org board software?) that the TAT page refreshed automatically every time you went back to it, which I always liked.