From someone who uses mixi, I can comment on a few reasons as to why they'd prefer it against Facebook:<p>* The Japanese are big fans of anonymous<p>A lot of big sites in Japan are that way because of their anonymous nature. 2ch is HUGE in Japan, because you can write whatever you want and for a majority of users it's all anonymous. Yes, you can make yourself known to others, but it's highly frowned upon. Another site that utilizes this is Nico Video, a site which lets users comment on videos anonymously.<p>Mixi holds to that as well, though a bit differently. There are many users who utilize pseudo names to mask their real identity (myself included in fact). What you can hide from others is customizable in a very simple way. Your birthday, where you live, what your hobbies are.<p>Then all your content has privacy controls as well. Everytime you post something you can decide who gets to see it. Your friends, your friend's friends, a specific group of people, or no one. While facebook allows this as well, my opinion is that Mixi makes it very easy.<p>* It's about going with someone you trust<p>The Japanese are big fans of going with things that are close to their circle of friends, or very established. Mixi is a Japanese company that originally started as an invite only service. That's a big part in helping it spread. "Hey my friend invited me so it must be cool since I trust what my friend says" kind of mentatility means people are more likely to signup and the effect spreads. While mixi is no longer invite only, they require a registered cell phone number (there are other ways but few people speak of them for fear of their abuse). This keeps things "inside Japan" further increasing the comfort of use.<p>As for the features, mixi emphasizes "friends of friends" relationship. When you visit someone's profile, it shows if they're connected to one of your friends. "Hey this person is friends with my friend, so they should be all right" becomes the frame of thought. This gives users a comfortable way to expand their network with people that share their interests (there are exceptions of course).<p>Not sure how to search for people to become friends with? mixi has a feature called 足跡 (translation: footprint) which lets you see who has visited your profile page. It also shows you if someone is a friend of one of your friends. These views usually come from people who are interested in something you said, or a friend told them about you. This means there's even a higher chance that the person shares your interests, and it's easier to become friends.<p>* The Japanese are HUGE cell phone users<p>Someone already mentioned it, but mixi has an interface tailored to the cell phones provided by major carriers. They recently made one for the iPhone as well. As having a mobile site is a bigger deal over there, it was part of the architecture from the start.<p>There are other reasons as well, but I think these are the big ones for users.