Add some message to make the submit button say 'processing' while it uploading files.

Another suggestion for the submit button - I note that when people have attached a number of uploads to their form, it can take a while to upload but there is nothing to indicate that it is uploading. Possibly adding something to make the submit button say 'processing' while it is doing that would be very helpful.

The submit button will show a "Please wait" if something like an upload is been processed:

You can customize that message at Preferences>>General>>Form Warnings:

 

Let us know if you have more questions.