CCF 2008 has the following improvements over CCF 2005
Better workflow implementation with the help of the Windows Workflow Foundation.
Enterprise grade Single Sign-On which help agents to access multiple systems with a single login.
Better development support with such tools as a hosted app. toolkit, security extensions.
End user portal built on top of MOSS 2007 that allows managing end user accounts.
Overall, CCF 2008 is a much better version with improvements in all major areas of prior CCF. It integrates portal, phone, email, fax, IM and chat in a much tighter fashion.