Some of you might have noticed that after the WordPress 3.0 upgrade there seems to be some kind of problem with installing/upgrading plugins via FTPS (SSL).
Could not create directory. /public_html
I am not sure why this bug happens, but here is a quick fix to get you going.
Open FileZilla or whatever FTP client you want to use and navigate to your wp-content directory, check for a updates folder. If you have such a folder delete it and create it again. Now CHMOD it to 777. Try updating or installing new plugins in your WordPress admin. In most cases it works as a charm.