When we have originally started the community forum in 2004, there was a lack of ASP.NET based forum/blog applications, thats how we ended up using phpBB. Like most LAMP applications, it was free but clunky. Upgrades were painful because they have always managed to break mods and skins, furthermore MySQL databases have a nasty habit of getting corrupted all of the sudden. Needless to say, we are happy to use CS for our community site. CS works very well in our environment and provides the flexibility we need.