Asif Rehmani (MVP and trainer) published this really useful post on EndUserSharePoint about SharePoint Designer 2010!
He uses 10 highlights to explain that SPD has got a lot of enhancements in this recent edition!!
He also has some stuff on video..
The highlights are:
1. New User Experience with Summary Pages, Ribbon and Quick Launch navigation
2. Creating SharePoint Content structure
3. Configure Site Security
4. Create Content Types and attach to Lists directly
5. Create Site Assets for your site
6. Use XSLT List View web parts to show dynamic views of your data
7. Connect to Data Sources outside of SharePoint
8. Create External Content Types using Business Connectivity Services
9. Create Powerful Reusable Workflows
10. Restrict SharePoint Designer usage as needed
If you want more news about SPD, check out this page on the msdn Infopath team blog !