Today Raymond Chen has signalled an interesting tip on how to control Automatic Updates bandwidth usage and reduce the resulting internet connection slow down.
The tips consists of configuring the Background Intelligent Transfer Service (BITS), the technology designed to manage the downloads of large files in Windows (with it you can download files in background, suspending and resuming the downloads etc.).
There are some cases where the Background Intelligent Transfer Service (BITS) has no idea how much bandwith you have, for example if you have a large LAN that shares a single DSL connection or if you have a network card that connects to a hardware firewall which in turn uses a dial-up modem to connect to the Internet (BITS sees your fast network card and can't see that there is a bottleneck further downstream).
According to Raymond, to tweak the BITS settings, you can fire up the Group Policy Editor by typing "gpedit.msc" into the Run dialog. From there, go to Computer Configuration, Administrative Templates, Network, then Background Intelligent Transfer Service. From there you can configure the maximum network bandwidth that BITS will use. You can even specify different BITS download rates based on time of day. Bookmarked! 
For who is interesting on using BITS technology to manage files download, on MSDN there's a .NET wrapper for BITS available. Check this link.