It's always bothered me how websites enforce heteronormativity. Facebook made a huge leap ahead in relationship status with its "it's complicated" status. Pownce seems to be trying to make a similar jump forward with their gender selections. Most are just for fun but hopefully a Transgender option will be put to good use by the community. There are still a lot of subcategories of transgender and hopefully they will come about at some point.
One reason many sites avoid complicated gender options is some ads can be targeted to gender and sites do not want to let people choose options that they can not monetize. While this makes perfect sense to marketers it just sounds dumb to every one else. If I was an advertiser and a site was serving my targeted ads to men and transgendered individuals were seeing the ad I would be upset that I was paying for that. As an advertiser I would push websites to have real world options for real world people. Conversely without the option on most websites the transgendered community effectively becomes invisible.
So weather they intended it or not Pownce is doing a service to the web.