Call the 10 you haven't heard from, people are neglectful, it's a fact.

Be sure to make a note to remove the oafs from your future guest lists. If people are too stupid or too lazy to respond, then I do not need to bother with them.

DP

I myself have forgotten to respond. If I don't do it the same day I receive the invite I sometimes forget. Give 'em a break, this is a busy time of year with school ending, weddings and graduations. Maybe just say, "I know you are busy so I just thought I'd call to see if you can come."

I agree with posieh. I try to respond immediately, but sometimes I can't (like if I have to check with other family members) and I have been late a few times.

These are your friends, so even though they really should have responded, give them a break and don't cut them from your list for one mistake. Just call or email and find out who is coming.

Have a fun party.

I still stick with dumping them from functions that have a formal invitation and a request for RSVP. I have had people not respond when we are using a caterer or booking a space in a restaurant. It can cause a lot of frustration at that time.

These friends are still welcome for small impromptu get togethers.

DP

Well... almost everyone came through on Saturday. I am so surprised they waited until the last day to reply. I still haven't heard from 4 families. One of them probably will come. That family has a reputation of not responding.
Thanks for listening!

As others have said, if a person doesn't rsvp on the same day they receive the invite, they probably will wait until the last day. As an example, if I need a head count by let's say the 15th of the month, I will tell people to rsvp no later than the 13th. Then I will call those that haven't responded on the 14th. We shouldn't have to make those calls, but people these days don't have formal "manners" with regard to invitations.