My visual editor wasn’t working for me after installing 2.8 and most of the solutions above weren’t working for me.
However, the following (finally) did the trick.
1. Disable ALL your plugins.
2. In the WP Dashboard: Tools > Upgrade > Re-install Automatically
Refresh your browser and the visual editor should reappear.
When I tried the automatic re-install before my plugins were on and I think this was the problem.
Judging from the amount of problems people are posting about upgrading to WordPress 2.8 this may not work for everyone but could be the solution that works for you.
