DD's party was last Saturday - invitations had been issued through the nursery (who might have messed it up a bit). Out of 24 invitations, 7 didn't reply at all and none of those turned up. If I'd assumed this would happen, I would have invited more of dd's nursery class but was too scared of having too many at the party (local softplay centre with a maximum of 25 kids).
Maybe next time I'll say "If you don't RSVP, we'll assume you're not coming". Would that seem rude?