Once in July 2011 in order to send me for training I've been given a Non Disclosure Agreement (NDA) to sign.
Among other things it had the following paragraph:

Inventions as Sole Property of [company-which-should-be-ashamed]

Any inventions, discoveries, concepts or ideas, or expressions thereof, whether or not subject to patents, copyrights, trademarks or service mark protection, and whether or not reduced to practice, conceived or developed by you in the course of your Placement or within one (1) year following the end of such Placement which relate to or result from the actual or anticipated business, work, research or investigation of [company-which-should-be-ashamed] or which are suggested by or result from any task assigned to or performed by you for [company-which-should-be-ashamed] shall be the sole and exclusive property of [company-which-should-be-ashamed]. You hereby assign to [company-which-should-be-ashamed] the entire right, title and interest to any such inventions, discoveries, concepts, ideas or expressions thereof and you agree to perform, during or after your Placement, all acts deemed necessary or desirable by [company-which-should-be-ashamed] to permit and assist it, at [company-which-should-be-ashamed]'s expense, in obtaining, maintaining, defending and enforcing inventions, discoveries, concepts, ideas, or expressions thereof in any and all countries. Such acts may include, but are not limited to execution of documents and assistance or cooperation in legal proceedings. You hereby irrevocably designate and appoint [company-which-should-be-ashamed] and its duty authorised officers and agents, as your agents and attorneys-in-fact to act for and on your behalf and instead of you, to execute any file and to do all other lawfully permitted acts to further the above purposes with the same legal force and effect as if executed by yourself.

So I refused to sign it.
The following day my manager spoke to me and sad:

"Why do you make it so complicated? It's a normal practice and we routinely sign agreements like this. Please consider signing it and let me know tomorrow."

I refused again and asked our company's lawyer for advice.
To my surprise he disagreed with my manager and commented that it's not a good thing to sign such agreement and that it's not in company's interests. Such agreements are way out of line.

As result the agreement was sent back and no employees were requested to sign it.
It just gone - after I spoke to our lawyer they agreed that no NDA is required.

Generally signing any NDAs would be wrong. See Three reasons why not to sign non disclosure agreements

Possible exception may be when NDA is actually to protect people's privacy.
For example if you going to work at hospital's data centre it should be OK to promise (in writing) that you're not going to disclose any patient's information.
Those who unable to made such promise are better not to access sensitive information.