BuddyPress.org

There were some changes in BuddyPress 3.0 to the activation process.

You’re most likely using a custom theme or you have overriden the activation template.

View the second point in this thread to fix this:

BuddyPress 3.1.0 is now available!

About the email, we updated the email to add the activation code. To see this update, you can reinstall the emails and that should allow your users to copy the activation code. View the first point in the above thread to find out how to do that.