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Uploading the zipped file to dropbox and unzipping it inside would save a lot of time and traffic for users. Some of the web services already exist for that (like this one http://www.quora.com/Is-the...
I think Dropbox should support more than the few very general file extensions. I'm having issues at the moment with a Zip file. It's I think trying to make me unpack and then individually add them which is kinda sneaky do to the fact plans are based on amount of space purchased our available. So allowing the whole Zip folder not unpacked would be obviously a positive to reduce amount of space taken up with additional folder to individual files.