One of the annoying things about JSPs is all of the dynamic (non-rendered) parts of the page still produce line breaks. This means that if you do a view-source, you'll likely see large blocks of whitespace.
The good news is you can get rid of this whitespace if you're using Tomcat 5.5.x. Just locate the "jsp" servlet in $CATALINA_HOME/conf/web.xml and add the following <init-param>:
<init-param> <param-name>trimSpaces</param-name> <param-value>true</param-value> </init-param>
I tested it and it works great. This begs the question - why isn't this on by default? Source: Struts Mailing List.
Update: JSP 2.1 adds the ability to trim whitespaces.