I found today my Dreamweaver CS4 hanging at the “Initializing Extension Data” startup screen. The resolution I found was to delete the site cache at “C:\Users\[user]\AppData\Roaming\Adobe\Dreamweaver CS4\en_US\Configuration\SiteCache”. I’m running Windows 7 on a domain so your path may vary a little.
After restarting Dreamweaver it updated the site cache and started working again.
I think it may have freaked out on a large cache after I deleted the actual folder.