When you are replying to a thread, you can click the "Notify me via e-mail when someone replies" box, right above the "OK" icon. Unfortunately, that requires you to check your emails to see if you've gotten a reply. I'm not sure if there's another way.

Note also that there's a "subscribe" icon at the top right of each thread. I'm not sure what it does, as I've never used it, but, it may do what you need...