dont agree with encosia personally, I think their only partially valid point is the caching.
Modern browsers allow more than 2 connections per hostname they all decided to ignore the RFC now, not only that but keepalive (default in all modern browsers) will allow objects from the same hostname to be sent over one connection, so obviously this is a time and resource saver as it means no extra dns lookups, no new connections etc.
I understand the point you made regarding jquery libraries, but I guess if its slowing down your site too much it may need a rethink.
Of course we dont know if this is the reason, personally I have not had any lag on here for many weeks. The lag stopped for me when someone fixed their sig which was causing me hangs. :p
I suggest next time someone see's lag, is to refresh the page with developer mode enabled in the browser and that will pinpoint which request is slow.