Of course it's pretty flawed - aside from the point mentioned in the article about forms signed under duress - even if the form states that it's not being signed under duress - it implies that consenting to sex once with someone equates with permanent consent. The form cited in the article contains the following clause:
"I commit myself not to ever stand on the witness box in court to testify against him or lay a charge of rape against him."
Split infinitive [flinch!] aside, not _ever_? Not even if, three years later, three days later, three minutes later, he rapes her? What woman in her right mind would sign such a form, except under duress? And what legal standing could such a form possibly have, anyway?
Still, it raises interesting questions about the nature, timeliness and duration of consent. If one consents, can one withdraw that consent - and, if so, up to what point? Is submission the same as consent? Under what circumstances is consent not consent?