We recently were debugging issues with our document uploader in Intervals and needed to throttle the bandwidth on our desktops so we could test the progress meter over our LAN (Typically, the LAN is too fast and the progress meter never appears).
We settled on using the Charles Web Debugging Proxy, which did a fine job of throttling the bandwidth down enough that we could use the Request Viewer to monitor the request / response headers.
A definite thumbs up for this product, as we were easily able to troubleshoot and debug the document upload in a matter of minutes.