There are two browsers currently in beta that begin to address some of the issues that make web sites slow, Microsoft IE 8 and Google Chrome.  I admit I have installed both of these browsers but haven't had much time to play with them to see how much performance improvement is achievable.  

Both browsers include performance enhancements with the downloading of external scripts.  Previously browsers would only download one external script at a time since these scripts need to be executed sequentially.  Needing to execute a script sequentially doesn't necessarily mean that they can't be download in parallel.  For sites with a large number of external scripts this improvement can significantly improve the page load time. 

IE 8 is increasing the default number of connections per host from 2 to 6.  The browser still makes connections to up to 3 different hosts which results in a staggering total of 18 connections.  An analysis of the impact 18 connections has on page downloads and possibly hosting providers was conducted by Ryan Breen of Ajaxperformance.  I have yet to test Google Chrome to determine what the default connections are and if this is configurable. 

It is still early days with these browsers but these enhancements seem to be a step in the right direction.