Having a Network+, Linux+, PMP, or anything else is great to show that you keep up with things, but are they really looked highly upon when it comes to getting actual work done ?
That's it, and it's completely unrelated to my job. I run Linux :). Why did I get it then? It was free from MS, required less than 6 hours of studying, and my boss paid me and my co-worker to go take the test.
I'm of the opinion that most certifications that aren't lab based aren't worth it. The only time it may be worth your time is for consulting or for an HR screen pass.
My current employer doesn't even like paying for certifications. They'll put you through all of the required training up until the point where you could get your cert (i.e. they care about the knowledge), but they won't pay for the actual certification unless you have a pretty good reason for doing so.
I don't think it makes you a good project manager, but it can be a way of weeding out people that are entirely clueless about project management.
It can also help if an organisation has standardised on a project management approach, so everyone uses the same names for Project Initiations, Business Requirements etc etc.
Certificates are neither necessary nor sufficient to be able to get a good job in my opinion and experience. Like you said, work speaks for itself. Certification on your Resume/CV might get you the interview call. But when it comes to hiring someone,what really matters is "can you get shit done and can you work with a team".