If you try to upload a file that is greater than 500k then google docs will complain with the message “We’re sorry, but we were unable to upload this document” and then suggests you copy/paste the document from your spreadsheet or save as html. It doesn’t tell you that the reason it failed to upload is due to the fact that the file is too big. The file size is mentioned in the requirements so it would be nice if the error message mentioned that. It does give you a sensible error message if you try to email the file though (which is how I discovered this)