IPB is a great product, but I still see some problems. The one I am going to let you think about is the loading speed of the forum page.
It can be speeded up just by letting hooks and plugins be loaded after the main page is loaded.
Doing this, users can have the perception of a rapid loading of the page becouse the main content has just been loaded (forums, logo, descriptions). After the page has been displayed, hooks and plugins can query the SQL server to retrieve the information needed to display their "additional" things (like most viewed topics, forums, and so on)
What do you think?