Found this on http://www.uscis.gov site, thought it was interesting. It is a document scanned to PDF, so I had to include a link, rather than actual text. Good read.
http://www.uscis.gov/uscis-ext-templating/uscis/jspoverride/uscisSearchO...
Disclaimer: I do not intend to marry a transsexual, not that there is anything wrong with that.