[Marco van Herwaarden]

Like Paul said, there is no way (well without rewriting half of vBulletin) to avoid this caching in vB 3.x.

Both Paul and your friend are somehow wrong on the memory usage per forum (or they could both be correct ). For each (sub)forum there is some information stored in the cache, you should think about things like Forum Name & Description (longer names/descriptions will use more memory), array of permissions for each usergroup (so more usergroups also mean more memory used), etc...

Next in this calculation is the number of online visitors and the number of pages they load. Each page will load another set of cached items in memory. So in the end it will be Cache Size * Number of Page Loads.

If you purchase vBuletin you will have access to all active versions, including the vBulletin 2.x versions. If you are starting a new board i would however try to avoid starting with an old version like vB 2.x at all costs. I would start by looking into alternatives for using that many forums. Using 2.000 forums is not only bad from a server perspective, but it will also very likely confuse the members and probably even prevent users from registering as they are overwhelmed with the number of forums.