This is almost an impossible question to answer, so I'll just give my perspective. I use perl to do some behind-the-scenes programming at work (data munging, log file analysis, some administration & automation). The powers-that-be (I'm a consultant working at one of the Canadian Federal Government departments) are fairly pro-Microsoft, so there's not much chance of me doing much stuff for end-users using perl.

I don't think perl is the "best" language to master if you want to get a job, if that's what you're asking (not flamebait, not starting a religious war). From what I see, C++, Visual Basic and Oracle are probably the top 3 job-getting tech skills. This isn't to dis perl, of course -- I try to use it as much as possible because it's ideal for a lot of the things I want to do. All I'm saying is that 95% of the people I know in IT primarily work with one of those three skills.

As others have pointed out, Java and perl don't really overlap much, so that's a bit of a non-issue. I'm not sure about PHP but I suspect that's probably a matter of choice.

I'd say perl is very healthy and viable, although if you start talking about perl to the average Pointy-Haired Boss you'll probably get a blank stare. And I'm pretty sure perl isn't in a "decline" at all.