SELinux saved my ass years ago, preventing exploitation of an outdated/vulnerable PHP application. Since then, it gets installed on every production server I deploy. Those who simply turn it off because it's a PITA are doing themselves a huge disservice.
An outdated version of a PHP application (which had a public vulnerability) was attacked, allowing arbitrary code execution. The "exploit" attempted to download and execute a remote file via TFTP. Ultimately, a "remote shell" would end up being installed on the server.
SELinux, however, prevented the TFTP transfer from happening. We saw this in the audit logs, investigated, and discovered what had happened (and, of course, updated the PHP application).
If the attack had succeeded, I'm convinced that it eventually would have ended up as a full ("root-level") compromise.
I believe NSA has a dual mandate. We are hearing a lot lately about their efforts to discover and use intelligence via electronic means, but I believe they are also responsible for providing guidance on how the U.S. can secure its own electronic communications--this is where efforts like SELinux and the guide to securing OS X come from.
We see the same kind of behavior in corporations all the time. "Sony" is both "Columbia Pictures", which wants to put invasive DRM in your TV, and "Sony Electronics", which wants to sell TVs without DRM so more people buy them.
And you can just look at the NSA's guide to securing Red Hat Linux.
It's not substantially different than the information you'd find in any other book about security. Anyone is free to review or comment on it. I don't find it plausible that the NSA would hide any tricks in that document so they could track you. At best, they might omit information, such as knowledge of a 0-day exploit.
As far as the NSA's published guide you linked, of course it is in the national interest for them to do things like that, and given the nature of a public document it would be foolish for them to put false or misleading information in it. That would be both bad, and comically obvious. I was thinking more along the lines of them promoting or mandating the use of encryption/technology that has weaknesses known only to them.
They were selected because they are the most credible; as the ones responsible for developing the most advanced cryptanalytic and signals interception capabilities possible they are also the ones best suited to identify attacks against which the U.S. must defend themselves, and provide suitable countermeasures.
For instance, NSA fixed a problem in what became IBM's DES crypto standard before the cryptanalytic community even knew what the attack was. So there's at least evidence that NSA takes that part of their mission goals seriously, and that NSA required the knowledge/skills/abilities of their "other half" in order to properly carry out those duties.
I would say most competent. I still think that it is a terribly conflicted set of roles, and that they've poisoned their position of trust. They still have the incentive to protect US interests from foreign enemies, including commercial ones as in the IBM example you cited; but, there is no longer any reason to think that those interests are protected from government agents with access.
Well they want to protect US data and get the data of other people...that is not exactly a conflict of interest.
Their trustworthiness on technical matters is a matter of public record--for example, as far as I know, Linux experts independently agree that SELinux is a very secure Linux configuration.
My orignal response was to someone wondering why the NSA can violate constitutional rights while at the same time open sourcing technologies for enhanced securities. My example of the DOD vs the NPS was to show that entities within the same organizational structure can have opposed goals.
[1]: http://en.wikipedia.org/wiki/Apache_Accumulo
[2]: http://accumulo.apache.org/