&gt;&gt; increase the number of parallel connections.
&gt; I believe that trick is to save bandwidth by not sending the (large) cookies that would normally be sent to the normal domain.<p>No, Internet Explorer (and other browsers) used to only allow a small number of connections per domain. Long running COMET requests ate up these connections, so if you wanted to simultaneously download multiple resources from a single domain, and reduce time to page ready, then you had to use multiple domains.