I had to sign a NDA when I became a "Fellow" three years ago. It was mailed to me (not emailed) so I don't have a copy to refer to anymore. But from what I recall it was actually quite sensible and not "over-reaching". It talked about not publishing other staff's employment details if you happen to learn it, not sharing passwords etc. As other people have said in this thread there are several genuinely valid and good reasons for having a formal agreement. NDA is not inherently bad.
On the other hand, I have been presented with a contract for some work with one of Chapters - that was clearly just copy/paste from a corporate organisation - that included NDA sections. It also included several amusingly irrelevant sections about "returning company equipment" and even an actually free-culture-incompatible section about how I should "assign all rights" to the organisation, including copyright and any patents "current and future" related to my work. Needless to say I didn't sign that.
This being the case, I do agree there is a genuine need for a standardised and clear staff agreement - that is public - that the Chapters can use as a template and so everyone knows what the 'rules' are.
-Liam/Wittylama (no longer a WMF Fellow)