Bringing this back again because I would like to point out that despite all rumors to the contrary it appears that Microsoft do actually read some of these questions, and the feature to have two working excel spreadsheets open for viewing and working on at the same time was added in Office 2007. Very useful for copy and pasting from one sheet to another or just to have information on hand for studying differences.
Excel 2007 View - Arrange all.

Now if future office programs would bring back Office 2003 voice recognition, that could be sweet.

from Chrissie