Software speed is of vital importance. Forum Software is notoriously fickle. Talk with users before making any decisions. User statistics and tracking are of vital importance for prioritizing future forum features and enhancements. As is the case with other types of software, there is not always a close correlation between the price of a package and its value.
Software packages requiring new or greatly expanded platforms can become very costly.
The highest costs associated with forum software are connected to maintenance. Investigation of true support costs is of high importance. Some packages come with open architecture and template language capabilities making them very customizable. Internal search capabilities increase in importance as the size of the forum and forum archives increase. That said, forum software decisions are very difficult to reverse, and thorough up front due diligence is well worth the effort.