By joining the forums, the mailinglists, blogs etc you are able to interact with a lot many guys who are using the same product as you are. This way you have a knowledge pool that you can use and learn from.
You can also start delving into the code and help in identifying the areas where code-documentation is lacking. Do this constructively.
You could even write your own comments in the code and check it in.
You could get yourself trained by the team and start working with the product.
Subscribe to the support package and ask queries that are answered within x hours.
Participate in other related forums and post your views.
Over a period of time, you will get to know the code better and better and then you need not get dependent on anyone. This will add value to your organization as well as you can customize the product to your need.
This is a very big value-add.
Join when the code-base is smaller. This will help you keep your reach in control. Not that you cannot trace it later, just that it will remove quite a lot of effort if you join early.
