Strategies for using the debugger with complex applications

Hello,

I'm curious about the strategies that others use for running more  
complex applications in the debugger. A content management system for  
example might require session data and user input in order to run it's  
code, all of which gets processed along a journey through a large  
stack.  How can I do 'something' in a browser and then run that same  
request in the debugger?

I see that Apache::DB does something similar where you can initiate a  
request in a browser and then control it in the debugger. But what if  
the app is not running mod_perl?

Thanks
Andrew