A page using XMLHTTP to test HTTP connection handling for difference browser. Nice to try if you write AJAX application

http://www.mnot.net/blog/2006/01/23/test_xmlhttprequest
http://www.mnot.net/test/xmlhttprequest/

Also there is a browser compatiblility discussion

http://www.musingsfrommars.org/2006/06/howre-we-doing-now-ajax-browsers.html