Everybody knows that running a forum is easy and hard.
The easy part is installing the software and seeing it work in your browser. Your database is small and it slowly grows during time as you setup your boards' categories and forums. Have more members and when they start to post.
The hard part is managing the board, your members and their posts. Keeping it active by providing content and optimizing your source code, features, options and settings.
The database can grow up to 100mb for a small site, or even above 1000mb for bigger sites and once you hit a million postcount you can be pretty sure your database is getting quite big, especially because of the attachment table.
So, how are you doing? What is your database size and how are you handling it? Are you still able to make a backup through the browser or are you running into errors and need phpmyadmin with gzip turned on; or even require mysqldump to do it properly.
The vBulletin Fan web site is nearing 100.000 posts and just hit 200 mb and attachments are currently stored inside the database.