getResponseHeader always returns null. Seems like a pretty big bug in the HTTPClient class (tested with 3.2 SDK on ipad).
Hey Kyle. I had the same problem. There is a work around for the getReponseHeader() problem here: https://appcelerator.lighthouseapp.com/projects/32238/tickets/1502-httpclient-problems-with-header-parsing-and-responsedata-in-onerror-handler
See the part by Brion on using a reference to the original object instead of 'this'. Works for me in 184.108.40.206 on OS4 on the iPad.