We implemented hCard+XFN and FOAF this year and I can say that the hcard+XFN implementation was definitely simpler. I expected that FOAf would have matured by now, but it seems like an academic mess that isn't getting a lot of recent community support. 

Glad to see your kudos for Elgg. They were very early to recognize that social networks were going to be an important form of software along the lines of blogs, wikis, and message boards. 