Read the article people, the author clearly cites lawyers saying the wording is too broad and would be difficult to enforce because it would violate the Fail Labor Standards Act.
Even if it was an "In acceptance of this agreement, Dickbags, Inc. will provide the employee with a lump sum equal to his/her previous year's salary. In return, said employee will provide assistance to Dickbags, Inc. for a period of two years." type of situation, after a few weeks, it would be pretty simple to say, "I'm sorry, I can't recall." or "I believe it was X, Y, and/or Z." You're not required to remember everything you did, its humanly impossible so it's not like they can hold you to it.
This.
As long as it was a decent amount of severance, I'd take it and wouldn't worry about later.
If they ever called me, (and I actually answered the phone), I'd be suffering from some serious amnesia. If they kept pushing me and wanted too much, I'd file a complaint with the labor board as I doubt the legality of providing free help for 2 years.
I worked for a company years ago that went through a couple mergers, and I was given a severance package (5 months pay) if I stayed around for the merger. A few months after I was laid off, I got a call from someone needed help with their system, but I simply told them I wasn't an employee any more, and they would have to talk to their IT people.