As a information security professional, I've always seen the whole "security by obscurity" issue somewhat misleading. By repeating the mantra, I feel many people forgot its true meaning.
Security shouldn't RELY on obscurity. That's true. But it doesn't mean obscurity, by itself, doesn't provide security benefits.
There are many examples where this is obvious. For example, would you publish your network topography on your public website? Of course not. Even if you were convinced that its security and access control are air tight, the cost of keeping such documentation "obscure" is negligible versus its usefulness by a potential attacker.
The problem arise when obscurity is used in lieu of proper security. Unfortunately, it still happens too often. But while the presence of obscurity may be seen as suspicious by an outside party trying to evaluate the security of a system, it shouldn't be considered as evidence of its insecurity, as it sometimes is.
Finally, I understand the "many eyes" argument, and how public disclosure of the security details of a system can help improving it. After all, nobody would think about trusting a crypto algorithm that hasn't been made public and scrutinized accordingly. But this logic cannot be generalized for all systems in all context.