For those of you with some of the largest forums (or other large online communities out there), what are the biggest challenges that you face? How have those challenges changed since you started out?
For me, the biggest challenge when we were small was recruiting new members, and now that we average well over 500 new members every day, the biggest challenge is maintaining that sense of community and making sure new users don't feel too overwhelmed to join in. We have a very high conversion rate when it comes to filling out the registration form, but that rate decreases when it comes to email activation, and decreases even more so when it comes to actually going ahead with that first post.
I'm also curious about any technical challenges big board owners face. We currently spend a small fortune a month on web hosting fees, and our server still gets taken down by malicious traffic and DDOS attacks.