I've discovered at least 3 discrepancies between the way reporting services renders a formatted number in a web browser and the way it appears in an export to Excel.
Format code: #
Web browser: renders non-zero numbers. Zero is blank.
Export to Excel: values show up as “#VALUE!”
Web browser: renders non-zero numbers in decimal format if the number as a decimal. If an integer, the “.” is not present
Export to Excel: renders the “.” always. In the case of zero, just “.” shows up. Ironically, this does not error which I would expect based on the previous example.
Web browser: renders positive and negative numbers as percentages, zero values as nothing.
Export to Excel: renders only positive numbers as percentage. Negative and zero values as nothing.