1. Inexperienced entrepreneurs
2. Big companies
If you have to sign one, make sure it's (1) mutual, (2) doesn't include non-compete language, and (3) expires. If you want to cheat, add (4) confidential information must be noted as confidential in writing or by email within 24 hours of being communicated. No one is going to do that. :)
And run NDAs by a lawyer, especially your first few. They'll talk you through the process of evaluating them.
I wouldn't sign the linked document, personally. This is pretty severe: "no person listed as a Participants may knowingly or unknowingly profit or benefit from the concepts, ideas, thoughts or information communicated or shared by any other Participants, unless hardcopy proof exists in a common medium used for communication that this information was either possessed prior to the date of this meeting by a person not listed as a Participants, or was created, refined, possessed or owned by the Participants prior to the date of this meeting, or is common knowledge."