After you use Adobe Dreamweaver CS4 on Mac OS 10.7 Lion, there are multiple entries for the application in Keychain Access.
This issue is a known issue with Mac OS 10.7. There is no negative impact to having multiple keychain entries for Dreamweaver, so you can safely ignore this unexpected behavior.
This issue does not occur with Dreamweaver CS5 or CS5.5. Your Mac OS keychain is used to securely store the user name and password for each of your Dreamweaver sites.