As far as a debugger tutorials, sure, the relevant perldocs are voluminous; but the few tutorials which I have managed to find demonstrate the same handful of examples which are mostly basic usage.
If you want to do anything non-trivial with the debugger, or if you find yourself poking around the perl5db.pl and DB.pm source for whatever crazy reasons, or if you find yourself wanting to extend the debugger and/or customize parts of it, you're pretty much on your own.
There was an engineer over at Yahoo who documented the debugger in much greater detail and clarity than in the perldocs(IMHO). Have a look at it here
I found it enormously useful in figuring out how the debugger works and in getting more out of the debugger.