I have been working with Sage ACT! since 2007 and what I have been observing is that with every new release a lot of new features have been added and enhancements are made to existing functionalities.
A few to list: Performance improvements, Networking enhancements, Tighter integration with Outlook, Integration with Email marketing, Writing Advanced queries to Groups/Companies, Customisable opportunities, Smart tasks, Compatibility with new technologies etc.