First let me address the issue of bandwidth ...
I've never had a problem. My account has 1.5 TB of monthly transfer. I have plenty of transfer. And even when I had only 100 gigs of monthly transfer I had previously uploaded files of between 35 and 70 MB via ftp without a problem. Remember, these are media files we are talking about - video files. In terms of downloading, they download a small portion to a viewer and begin to play while the remainder continues to download.
Here is a copy of my php.ini file:
register_globals = off
allow_url_fopen = off
expose_php = Off
max_input_time = 60
variables_order = "EGPCS"
extension_dir = ./
upload_tmp_dir = /tmp
precision = 12
SMTP = relay-hosting.secureserver.net
url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=,fieldset="
[Zend]
zend_extension=/usr/local/zo/ZendExtensionManager.so
zend_extension=/usr/local/zo/4_3/ZendOptimizer.so
I don't see that variable to set anywhere. If I can just copy and paste it in, what units is the variable looking for. In other words, if I set
upload_max_filesize=1000
Will that set the upload_max_filesize to 1000 megs or 1000 bytes?
Also, if this particular variable trumps what you set in WPMU, why bother allowing a user to change things in WPMU?