When i was looking for forum software, people kept saying to me that i wanted to make sure that the software was upgradable to Vbulletin incase the forum really took off.
Why can't other forum software deal with large forums, i'm sure its just a myth that they cant.
http://rankings.big-boards.com/?filter=SMF,all
More important than the software is how well the server can cope. SMF is designed to run lightly, so it will run well for small forums, and it will run huge forums too.
I think someone needs to make a review site that tracks the efficiency, features, ease of maintenance for each of the popular boards.
Have gone through Invision (when it was free), phpBB now looking at SMF. There are so many issues you often don't find until you are already running a board and have users depending on it.
Unfortunatly for someone to do that, they would probably be a big forum user / admin and then as a result would probably be bias to the software they use.