Am I missing something here? surely WSUS does this for you? I can only think of is that WSUS downloads and push's the updates out where by the WUA devices only download an update when needed ...
Yes, windows server can do the update caching for windows updates, however the Update Accelrator for IPCop can cache from:
*adobe
*microsoft
*apple
*symantec
*avast
*trend micro
*linux
*and even "other"
So with WSUS you can ONLY cache microsoft updates.