At Otterbein, we have "accept with regret". Since our parties are on weekends during the school year, some girls have to work/participate in "insert extra curricular here". While my honest opinion is that since the dates are given to girls when they sign up for recruitment in fall quarter they should try to schedule around those blocks of time, I know that this is not always possible for one reason or the other (religious observance, night class, whatever). After open house, you can recieve up to 6 invites, but only accept 4. If, for whatever reason, you cannot make it to the party of one of your remaining 4, you mark "accept with regret". This COUNTS AS ONE OF YOUR 4 PARTY CHOICES. Same goes for final party, only accept or accept w/ regret 2 out of a possible 4.
With having a later recruitment, accept w/ regret doesn't hurt the PNM as much as a fall recruitment, I think, since an active sister probablly knows the PNM from campus or has heard of her through campus activities, plus the connection/introduction at open house.
Buy the ticket, take the ride!