We just rolled out a new replies notification feature. You'll notice that there is a small envelope icon next to your name at the top of the page.
Every 30 minutes, we check to see if new comments have been added to your posts, or if new answers have been added to your questions. If so, the envelope will light up. Mousing over the envelope will explain what's going on.
Clicking on the envelope in either state will take you to your recent activity page. This page is private to you.
The focus of the recent activity page is things other Stack Overflow users have done to your stuff! In other words, if users have...
- added answers to your questions
- commented on your questions or answers
- edited your posts
- voted your content up or down (or otherwise) affecting your reputation
It's visible here.
We also have a handy topbar notification if you've been away from Stack Overflow for at least 24 hours. It links to the exact same page, but will tell you exactly how many new answers and comments your posts have generated while you were gone.
We're still refining how the recent activity page works, but hopefully this will make it easier for you to find (and possibly respond) to the answers and comments left on your posts!