As far as a guild being to large in part as to do not so much with to many members but how they can accomodate the amount of people they have at one setting and also fire codes and laws in place in an area. The only negative I've seen with limited members is not even that problem but a social group that think they are better than you because you don't meet there standards or live on the right side of the track or are not of the right ethnic group.
With us it would be being able to find a venue that could accomodate say more than 50 or so folks at such a meeting I believe. We however have no such limits on how many members can join a guild so it will be interesting to see how we solve the problem of needing more room once we hit 100 or more members.