What's new in version 2.0?

CiviCRM 2.0 provides signicant code and schema changes to improve performance and scalability.

Other highlights include:

• Campaign Widgets: Now your supporters can promote your fund-raising campaigns by adding a flash
  widget to any web page. The widgets provide a real-time display of current contribution results along with a direct
  link to the contribution page.
• Tell A Friend: Make it easy for contributors and event participants to spread the word to their network by passing along their personal comments and links to your campaign pages. Friends are automatically added to your database and "recruiting" activities are credited to the senders.
• Custom Searches: Developers and accidental techies with a bit of PHP and SQL knowledge can create new search
  forms to handle specific search and reporting needs.
• Pay Later / Pay by Cheque: Now you can give online contributors, members and event participants the option to pay by
  cheque.
• Standalone version with OpenID support: Now you can install CiviCRM independent of a CMS. Users can login with their OpenID.

From CiviCRM 2.0 Product Sheet (.pdf file)