Yes I did that once but it was quite some time ago our use was quite high even back then. What it can't show is how much time is wasted by users that have to sit there twiddling their fingers while something downloads.
I believe if you log a call with BGFL, they can actually monitor your school internet usage levels at peak times of the day, just to see how much your connection is being used.
It may well be that a web based MIS system wont have a very high bandwidth requirement (I simply don't know one way or the other) but the issue is that its using the same connection as all of our curriculum users which already puts our connection under strain. If we are not careful we could have admin staff unable to complete their jobs because year 6 are streaming videos for the kids to watch etc...
I suppose Education City is a little different as it renders Flash on the local workstation. Future versions of SIMS and Progresso are either going to be PHP based, or most likely ASPX based, i.e .NET Framework 2+ and generally speaking this shouldn't be too resource hungry on the workstation.