Jim McGimpsey is a MS MVP and a Mac specialist. I just found his web page today. He lists some of the bugs/limitations related to XL 2004 and with discussions about each:

McGimpsey

McGimpsey's list:

General and Setup
  • Pasting from XL04 to another application fails (MSKB)
  • Can't open XL2003 files (MSKB)
  • "Permission for this document is currently restricted" when opening XL03 files (MSKB)
  • "Smart formatting" doesn't format a range of date cells


Worksheet functions
  • COUNTIF() only counts used range


Charts
  • Chart labels may overlap (MSKB)


Printing
  • Text in Outline format prints as Bold (MSKB)
  • Borders may not print (MSKB)
  • Double Underlines print as thick Underline (MSKB)


Userforms
  • LoadPicture method doesn't work
  • Range.Copy method doesn't Work from Userform
  • Focus problems with Userforms


VBA
  • Event macros are not deleted
  • Deleted or renamed procedures corrupt module
  • Range.Copy method doesn't work from VBE


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Okay, somewhere MS has claimed "cross-platform compatibility". Looks like there is a ways to go!