I've been on steemit for about a month (as mountainherb).  It has some flaws, maybe not fatal but serious:

 - It's more a platform for content creators than a social media site.  Unlike FB or Twitter, for example, you really can't post a brief thought and start a conversation with friends/followers/the universe.
 - There is an enormous amount of junk, with no good way to filter it out AFAIK.
 - There is no mechanism for contacting another steemer directly.
 - They separated the actual conversational aspect into steemchat, which is even worse for junk and lack of filtering.

Overall, I like the idea of it, but I don't find it very useful, user friendly or valuable.  Just my .02.