I think the characterization "o strongly promoted as the best calculation program ever" is definitely not true. I really like Numbers but like any other tool it has its strong and weak points.
The main weaksnesses are:
- cannot handle large datasets greater than 65000 rows and 256 columns (roughly)
- does not support all (or similar functions) the excel does
- no built-in scripting (relies on Applescript) so script additons to a Numbers document to not export to Excel
If Excel compatibility is paramount to you then my suggestion is to use and stick with Excel. It is too much trouble to keep crossing that bridge.