Interesting read from National Review Bench Memos
The Republican signatories' agreement to oppose cloture reform is contingent (both expressly and as a matter of basic contract principles) on the Democrat signatories' living up to their end of the bargain. The fact that the MOU contemplates that each signatory will use his own discretion in determining whether extraordinary circumstances exist does not mean that Republican signatories will need to defer to a Democrat signatory's determination. On the contrary, it means that a Republican signatory is free to use his own discretion to determine that a Democrat signatory's determination of extraordinary circumstances amounts to a violation of the MOU. And the nomination of any person who elicits fewer Democrat objections than Brown, Pryor, or Owen should not constitute "extraordinary circumstances".
Someone else said: "This is the essence of the agreement: The Republicans have agreed not to ban the fillibuster -- as long the Democrats don't use it."