drooh - 10:19 pm on Jan 8, 2013 (gmt 0)

I would think it would be nice for the user to know something is happening when they click submit and the upload progress begins, and the form sits there for 20-30 sec...

Also, the average user wont have anything disabled, someone who knows how to do that will probably know that uploads take some time and will be patient.

The idea here is that you give the user some kind of notice that the form is working and not just frozen causing them to hit the back button or click elsewhere.