This is a common problem in large workbooks, especially ones that have
been used internationally
There is some good info here:
http://support.microsoft.com/kb/213904
There is a commercial tool for exactly this here:
http://www.rowingservice.com/quarrell/QAid/
In simple terms you need to reduce the number of format combinations. If
you have lots of charts that would be the best place to start - set all
axis fonts to a fixed size.
After that go through the workbook simplifying formatting eg by only
using a single font, by only using 2 or 3 background colours etc.
If you are copying in from other workbooks do a paste special values or
formulas rather than a normal paste as that often brings a load of
formatting junk in.
Cheers
Simon
Excel development website:
www.codematic.net