While I was catching up on the development of IE8 I found this over at the IE blog:
In IE8 Beta 1 we also increased our per-server connection limit from 2 to 6. What this means is that in IE7 and below pages could only download 2 elements from a given server at any one time. Increasing that limit to 6 allows sites to download 3 times as much content in parallel, which should translate into faster page download times when bandwidth is available.
Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy.
Granted, the HTTP specification was written a long time ago; internet connections and servers have become much more powerful. So, will it matter?
My main problem is that the decision has moved from server administrators to browser developers. If you are a server administrator it is easy to split up content so that it appears to be coming from multiple hosts to get the same result. You know more about the content that needs to be delivered and how it should be partitioned.
If IE8 uptake is quick I guess some popular sites will see some negative effects of the 300% increase in the number of connections.