FYI: As you suspected it's not cool to say fixie, except for ironic purposes. Like, you could call a newspaper article on the fixed gear trend "another fixie expose" but you wouldn't refer to your own bike as a fixie.

The best advice i think there is for a new fixer is, your knee cartilage will get good and strong from fixed riding but not if you overstress it and fuick it up. So go easy to begin with---quit riding for the day if your knees start to give off a bad vibe. Try not to let em actually start hurting.