Steam has announced some kind of thing that does a clever something or other that tweaks this thing and tinkers with this other thing, and the result is that downloads are faster. Or, at least, they will be. It involves caching at ISPs, more firewall-friendly protocols (downloads will be coming via good ol' HTTP ) and, best of all, a system that means more incremental patch downloads, instead of having to re-grab big huge chunks of game. Here, I'll let them explain - as well as share some bonus good news.
With the Steam content system that’s been in place for a few years now, if an individual file on disk were modified by a game update, your client had to download the whole file. That can be painful when the file in question is really large. The new system supports delivering only the differences between the old and new files, meaning game updates will be much smaller overall.
Given some games do merrily contain multi-gigabyte single data files, that does sound like good news. Better news still? "Soon, Dota 2 will be delivered using it." Ooh! Ooh! Ooh. With other rumourflies a-buzzin' around mutters of a possible unveiling soon (some are even claiming GamesCom), DoTA2 suddenly seems to be looming large.
More details on the new system here. They also reckon Steam will be able to shrug off high demand a lot more competently as a result of this system. If that means an end to popular games downloading slowly or being deemed temporarily 'not available', I am all for it, yes sir.