Thanks Tim. You hit my weak point, in that I got out of numbers quickly as I needed to produce something, at the time. However, in the light of your e-mail I certainly went back today (at Macbook level) and converted back and forth between numbers and excel formats.
However, taking a fairly standard model, for me, using some excel (neo-office) features, I got conversion failure report on several features:
* Print area isn't supported and was removed
* Print setting for row and column titles aren't supported and were removed
* Form controls such as check boxes and scroll bars were removed
* Data validation isn't supported and was removed. The cell values were retained
* Pop up menus in cells weren't imported. The cell values were retained.
* Sorting criteria were removed
* Unsupported border styles were mapped to solid borders.
Also, another factor. In taking over files from someone else (a leaver) in my organisation, I got hundreds of numbers (and pages) files. Unfortunately, I can't recirculate without conversion (time and effort), to others of the many members! Not a good situation, hence working to a standard of xls (and doc).