Based on my experience with Mixi and Facebook, there are a number of differences between the two, probably due to both cultural and technical differences. I touch on this in this related article on the problems with Mixi.

Platform: It seems like a majority of people use Mixi through their mobile phones, updating their status, writing their blogs, and adding/uploading photos. While Facebook users are increasingly using their smartphones to do the same, I would say that the bulk of the users are still accessing it via web (computer).

Blogging: Mixi’s main feature used to be the blog, so this at least was more emphasized than Facebook notes. Mixi blogs tend to be more personal than Facebook notes, more like a diary than a notice or an advertisement, but usage highly depends on the person. Some people used to write multiple times a week, or even daily; however, this no longer seems happen with the introduction of more quick update features like Mixi voice.

Relationships: Some users on Facebook seem to take advantage of it to keep family in touch. I don’t see much of that on Mixi, maybe because older generations are not on it as much. In addition, people occasionally write diaries about their girlfriend/boyfriend issues because they are either not on Mixi or connected to them.

Status updates: Users of both platforms have migrated to using the Twitter-style status update feature once the idea was stolen and implemented. In Mixi in particular, people use this more often than blogging now.

Profile/privacy: Nearly no one in Mixi uses a real picture of themselves for their profile, while most facebook users do. Mixi users also tend to not disclose their real name and often keep their profile/diaries/pictures private to the first degree of friendship. Mixi profiles often don’t contain school or company names, although given the option to do so. Profiles seem secondary to other features on Mixi, since you usually access another person’s diary/photo/etc first before their profile, due to the way the site works. I won’t go into the privacy issues that facebook has in the first place.

Commenting/Liking: Probably due to real-time UI updates that Facebook, Twitter, etc. provide that Mixi doesn’t, there is a lot more active exchange between users on Facebook. Also, as a default, Mixi users don’t get emailed every time someone comments on their diary, status, etc., so you have to be actively accessing the site to get that much activity. There is also no equivalent of a “wall” on Mixi, limiting random public messaging. There is just a one-time “introduction” feature where you write about someone on their profile (usually nice things).

Apps: Seems similar to me. There is definitely a Farmville equivalent on mixi, etc. I know people use it on both, but I can’t speak of this as much since I tend to avoid them. I also find access to apps somewhat confusing on Mixi…

Photos: The interface on Mixi is annoying, but people do still upload them, mainly from their phones. I think there isn’t as much commenting activity on them, perhaps because there is no tagging feature.

Location: Both seemed to have just copied this feature, and it seems like only select people are using them in both cases at this time.

Other: I personally use mixi more for their aggregated news, just reading up on popular news and articles. I use facebook to stalk people and dig through their dirty laundry.

Facebook is based on the idea that you want to replicate your real life social network online. This is fundamentally counter to the presuppositions of Japanese internet behavior.

There are other specific platform challenges, but there isn’t really a ‘real name’-based SNS in Japan that shows that the Facebook concept will even fly.

That being said, many Japanese — who have foreign friends or are generally less squeamish about their web activities being seen by people they know — are joining Facebook and using it in the international mold.