@The_Idiot Re: Sharing such files over the LAN should help...
Inconsiderate, arrogant fuckers. That's my metered bandwidth your sharing; ask me first.
BitTorrent asks me first.
OS X Caching Service asks me first.
Linux caches and proxies ask me first.
Even Flash asks me first IIRC, FFS!
Yes, local network caching is a good idea. I think Macs should do that too, without you needing a server. But this M$ behaviour puts Apple's hubris to shame.
Notice here that the peer-to-peer aspect means you can't really control any client once you've given it access. So, together with Wi-Fi Sense, you have even more good reasons to refuse Windows entry.
UPnP IGD (or the nicer NAT-PMP/PCP) isn't evil. It's broken hosts and NAT that are. Fix and get rid of those so your apps can't open up backdoors or fail to function, respectively.