1). Add. Faster.
Look in the lower right corner to see a quick preview of the sum of your currently selected cells.
2).A new tool for freezing rows and sorting the spreadsheet
3). Use any browser to read Google Docs
4). What are my collaborators looking at?
When multiple people are working in a spreadsheet at the same time, cell presence indicators show you where they are

http://www.google.com/google-d-s/whatsnew.html

But they still hate Opera. ¬¬