Advanced Excel Services:
MS wants Excel to be the BI analysis tool of choice: adding MDX & write back for 2010
Excel Services 2010 will have increased fidelity; if there's a picture embedded in your Excel sheet and you publish it, nothing will be stripped
Filters in Excel now have search capability with auto-fill
Use 'named sets' to save filter views of data so that you can re-use the views
easily convert pivot table cells to formulas.. one click
Interact with Excel spreadsheets on the web using slicers, this will give end users great flexibility to create dashboards
In 2010, you can type directly to the Excel sheet by enabling the feature in the web part properties
Modifying a published Excel sheet that has linked web parts will automatically update the other web parts (for example, charts) - with no page refresh :)
Using REST, you can send a range of cells on an Excel Services sheet to someone (via email). Just click and drag to select and choose to send the link. When the other user clicks the link, all they see is the range of cells you selected. No coding - SharePoint does it for you.
