The subject says it all. I can drag .csv and .xlsx files into the Numbers for iCloud beta desktop, but when I try to drag a spreadsheet created with the latest version of Numbers it deems it a file that can't be imported.
I'm having no trouble uploading iWork documents to iWork for iCloud in Safari.
Ultimately, the easiest way to save iWork (Pages, Numbers, Keynote) documents to iCloud is to save them to iCloud from within the application (File > Save and choose iCloud).
Retrieving data ...