For HTTP 1
For HTTP 1.1 it’s limited to 2, HTTP 1.0 is limited to 4:
http://www.mydigitallife.info/2008/06/24/tweak-inc …
Interestingly, IE8 will be allowing 6 simultaneous connections:
http://weblogs.asp.net/hpreishuber/archive/2008/07 …
I’ve seen the same argument used for single image mouse-overs. i.e. You should use 1 graphic with all the image states (normal, hover, active, etc) and change it’s offset for the different states:
http://magnetiq.com/2006/08/27/using-less-images/
The difference is minor but it can certainly help.