Today, I needed to send an Excel-file to a customer, but it was too large according to his mailserver. Of course, there are several solutions to that, but uploading the file to MegaUpload or RapidShare wasn't exactly what the customer had in mind :).

But when you keep in mind that every Office 2007+ file is basically a compressed folder (zip), you can compress the contents of any workbook dramatically. Here's one example: an Excel file containing the AdventureWorks 2012 relational model is around 44,7 MB.

Extracting this zip in a folder gives me the following list:

Then, I re-zip these files with a higher compression rate (for example using 7-zip on the 'Ultra' mode) and rename the resulting file to '.xlsx':

The result is a workbook dramatically reduced in filesize, but the contents are still the same (plus, it can still be opened with Excel).