I know one Forum that plays with it's member count hoping that everyone will flock to see what thousands of others are seeing.
Don't do it. It backfires when the scheme becomes obvious. Your Forum may build slowly, but it will be solid.
I have only been up for a few days and have 30 solid members. I've deleted 3 who did not activate within 48 hours. Some Forums activate a user manually to help the member count, even if that member never returns.
I've deleted 2 troublemakers who I knew from their static IP. I will clean my memberlist on a daily basis. You will never see 5,000 members with 98% marked 'Yet to Post'.
Patience. The turtle won the race.