NDAs refer to nondisclosure agreements. They are contracts -- in this case, between Apple and would-be developers -- that prevent those who have been granted beta access to early releases of Apple's software development kits from discussing any aspect of the SDK in public forums.
Apple has pulled this NDA on us a few times before, for iPhone SDKs that anyone and their brother could download and look at freely. I'll say it for the record: NDAs on new iPhone OS SDKs are a bad, bad thing.
These NDAs provide no protection against competitors discovering Apple's proprietary secrets. Apple places no restrictions on who may sign up and access those materials. At the same time, they limit developer discourse outside of Apple's rather minimal members-only developer forums.
Under past NDAs, TUAW could not publish how-to articles or code samples, which was frustrating. The fundamental problem is not limited to this site, though. Developers couldn't tweet about their experiences, write about them on developer e-mail lists or otherwise engage in the kind of productive peer support that makes a development community thrive. Limiting discussion to a vendor-approved site where posts can be modded and/or deleted at the vendor's whim does not exactly cultivate open discourse.
Of course, we're talking about Apple. As avowed "Gearhead" Aleksandr Milewski puts it, "It's Apple. They'd NDA their customers if they could." So you can take it as likely that once again Apple is going to slam down an NDA on our collective selves. At least unless enough people proactively stand up and say: "We're mad as hell about NDAs and we're not going to take it any more."
So what can you do? Add your voice to this post. Leave a comment and express exactly how you would feel about Apple NDA'ing the upcoming iPhone OS 4.0 SDK. Tweet it. Status wall it. E-mail it to your friends and to Apple. File a bug report at bugreport.apple.com. Give some unofficial feedback. Post about it on your own blog and leave a link in the comments.
It's time to be heard. We're tired of REDACTED and we want change.