The Business Data Catalog is evolving into Business Connectivity Services (BCS), which allows you to connect to line-of-business applications, Web services, and databases. The amazing thing with BCS is that the Web interface allows users with permissions to update aspects of the data, and that data is updated to the back-end services. For example, if a user alters an item on the SharePoint site that is pulled from a SQL database, the SQL side is updated without the user having to be concerned with the infrastructure at all.
I'm especially excited about SharePoint Workspace; it brings Groove into the SharePoint world to allow for pulling lists and libraries offline to work and then resync when back online. Groove was acquired with Ray Ozzie a few years back and didn't see enough light in the Office 2007 release. But its phoenix-like rebranded resurrection in SharePoint 2010 as SharePoint Workspace is awesome.
Finally, if you are a true SharePoint developer (someone who reaches into the guts of SharePoint with tools like Visual Studio and SharePoint Designer, rather than just stick with the standard Web development tools), you're going to love the new Visual Studio 2010 tools and the new SharePoint Designer 2010.
Improvements geared to IT professionals
First off, the Central Administration site itself is welcome eye candy. The previous versions were scary, for lack of a better word: no graphics, with text and hyperlinks to strange new worlds for the newbie. But now, SharePoint 2010 has an attractive and less daunting interface. The ribbon UI is included to keep with the new theme, so that will take some getting used to for those who are accustomed to having all the links and options out in the open. But I believe you will find the ribbon groupings to be logical. For example, if you select a site to work on, the ribbon will switch to a Web Applications tab with groups that include Manage, Security, and Policy, and all your options are presented in those groups.
You'll also appreciate the Best Practices Analyzer, which does more than just show you where your site may be lacking. It also offers suggestions to fix those items and sometimes even the opportunity to fix those items automatically for you.
SharePoint 2010 improves usage reporting and logging features, as well as large list resource throttling to help provide more control over reduced performance from excessive lists and libraries that may be slowing your servers. There is also a new unattached content database recovery feature; it allows you to mount an unattached content database temporarily so that you can view content, make a backup, or export sites or lists -- without creating a recovery farm.