I was thinking about BITS, actually. Bandwidth reservation made me think of that. My mistake.
> QoS is something that sets packet priorities.
True. It's a network service that guarantees (or doesn't, depending on network resources) to applications that require it, that service quality (bandwidth, latency) doesn't go under a certain threshold.
This is where you get trollish:
> Obviously the ones for adverts are higher and all your non-important stuff gets put to the back. QoS also reserves bandwidth just in case something with high priority might come along, so you get ads faster than downloads and ads are the first thing to show up on the page when it starts rendering.
This sounds wrong, especially when you say that most QOS doesn't go beyond the average private router. As you say, unless you have a router that handles QOS and the routers on your route share the same policy, QOS is basically useless, but I believe also harmless, because all packets fall back to best-effort level, and no ad packets get the special QOS flags.
But even not considering that, I highly doubt your average browser will mark HTTP requests for ads with a higher QOS level, this sounds so very wrong that I don't even feel the need to explain that.
Why are you so angry with QOS? Do VOIP calls (not skype, eh) on your operator's network reduce your torrent download bandwidth? :D (now this is where I get trollish).