It would not surprise me to see little difference in the stored file sizes.
MS certainly realized that a significant file size increase in all the Office
apps would be an issue with many customers. So the XML is actually
compressed within the file. But I still have to believe all that code that
takes what used to be interpretted for display from the XLS format, now takes
a lot of new code to interpret an entirely new (additional) format.

Here is a good article on the file format, albeit rather basic.
http://office-watch.com/office/archtemplate.asp?v10-n18

Section 1,3,4,5 cover it pretty well.

"Dave F" wrote:

Wiley--

I haven't noticed any difference in file sizes.

But with XL, for example, it is routine for XL2007 to consume 200 mb or so
of RAM when using a file, which if opened with XL 2003 consumes only 50mb or
so of RAM.

Not sure if it's a function of the file or the application, but the RAM
demands that Office 2007 place seem unusually large.

"Wiley" wrote:

Dave,

I have not installed it yet, but all the reading I have done notes that the
default file format is Office Open XML format. Some tests I have done shows
that an XML created by 2003 is twice the size of an XLS file. My guess is
that there is moer RMA required for the file size and for the XML processing
that is an addition to prior versions. BTW, how much mre RAM do you see it
consuming?

"Dave F" wrote:

Just curious if any other beta testers of Excel 2007 or Access 2007 have
noticed that the applications use much more RAM than their Office 2003
equivalents?