This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
When you say "custom tag lib" are you talking about JSP tag libraries, or something else?
If so, then there's no difference than using any other JSP mechanism. Remember that JSP is evaluated on the server to substitute any active elements in order to send a good old fashioned HTML page to the browser. The result of any custom tags will simply be substituted into the page and the result will be sent to the browser.