I believe that most large boards are using vbulletin, as using UBB.classic isn't an option for the size boards they are refering to, and few are fond of UBB.Threads looks
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.