I can safely say that there has not been one event that I have planned where the host has not had to make calls to guests who have not replied by the response date. I do think this is incredibly inconsiderate on the part of invited guests but the fact is that it is not only ok, but necessary to call guests if they do not respond on time. Also, there are likely to be a few last minute changes so as the host you should always plan accordingly.
Again, some great advice. Thanks Always a Blogsmaid.