Go to the Settings link, located right next to the log out option in the upper right portion of the screen.
->Then, on the left side of the page that opens up, find the third menu box on the left side of the page, entitled My Settings.
-->Select the General Settings link, which is located under My Account.
--->Scroll down until you get to the Messaging and Notification section.
---->In this section you will see an option for "Quote Notification":
----->If you want to receive a PM whenever one of your posts is quoted, select the option for "Private Message";
----->If you would prefer to be notified by email (the email will go to the email address you used to sign up for BL), select the option for "Email".
------>Once you have specified how you want to be notified when your posts get quoted, scroll down and hit Save Changes.
This will only notify you when people quote your posts however. I believe you can also fiddle with your settings to receive a notification whenever someone replies to threads you create, but otherwise it is up to you to stay on top of replying to what people say in response to what previously posted.