Facebook is a useful site: it’s easy to connect with friends and family and keep abreast of their lives. It’s an easy place to make a home page. But it could be so much more, and I can’t get past some of their deep-seated issues. I haven’t quit but I have curtailed my usage (though I was only logging in every few days anyway).
There’s room for improvement on the site experience itself but the main issues to me are more cultural:
You don’t control your account and support is almost non-existent: if something goes wrong with your account or it’s automatically disabled in error it may be impossible to resolve. One day you may have lost everything…
The Internet is built around the idea of sharing information and linking from one site to the next, yet Facebook is designed to be your one-stop site, and only minimal Facebook information is available outside of Facebook without registering and logging in.
Many many privacy issues, e.g. Criticism of Facebook