For Excel in particular the list is actually really long. The big ones are flash fill (pattern recognizition for data cleansing), quick analysis (live preview of different analysis elements with your data), side by side Excel sheets, Chart animations, automatic PivotTable recommendations, automatic Chart recommendations, Data model (Powerpivot - in memory data analysis engine that allows creating relationships between data sources -db style), among 100 more.
I'm very curious to try the Windows version though, what are some of the bigger changes? (Aside from the better pivot tables, better sharing, and smart-fill on the product page).