To me, the debugger is indispensable, and I'd urge everyone to learn and use it.
Besides using "perl -de 1" to test any code snippet, there are many cases where the debugger is much better than print (of course, I print too, and log with Log4Perl). For example, if a script gets an array of files to process, and something is not right for one of the files, it's so easy to run through the debugger and change the array on the fly than to change the code. And when you are handed someone else's code, going through the debugger will reveal much more of the flow than print.
On a side note, I think php doesn't have as nice an interactive shell, it's one of the things I really miss when I do php.