Not that I'm a huge fan of Java as a language, but...

Currently Perl is supported on hundreds more platforms than Java. "Write once, run anywhere" is still a myth for Java, but practical reality for Perl.

This, of course, depends on what platforms you're interested in running your applications on. While Java runs on fewer platforms than Perl (although I don't think it would be hundreds fewer) it runs on several useful platforms that Perl doesn't run on at all (the opposite is of course also true).

I think you'll have to be a lot more creative if you're trying to come up with examples of applications that Can't Be Done In Perl.

How about anything running on the 100 million Java/Symbian devices that Nokia are going to be shipping this year :-)