Dropbox folder opens on computer startup - how can I disable that?

I am glad to report that I have fixed the issue of the Explorer window pop up. After performing the re-install process you provided (which in my case wasn't successful) I discovered that the real issue was a left over shortcut in my folder: %appdata%\Microsoft\Windows\Start Menu\Programs\Startup. I think this was left over from the time when it seemed to be needed to start Dropbox on startup.

Although I appreciate the reinstall instructions, there are several parts of this that I feel are  problematic.

1. The registry keys (not folders) to delete are also in the HKEY_CURRENT_USER hive at: HKEY_CURRENT_USER\Software\Dropbox and HKEY_CURRENT_USER\Software\DropboxUpdate
2. I would be more specific about the keys to delete because you don't want users to have a chance to delete the wrong key. If I use the Search (Ctrl-F) function, I will hit many more places where the word Dropbox is found, such as in other Keys and MANY Classes.
3. I install DB as a Std User. Therefore I was unable to delete the key in HKLM until I ran regedit as Administrator.
4. Add a standard disclaimer about modifying the registry.
5. Add a section to check for a shortcut in the Startup folder. Or other places where DB can be started that could be left behind.

After all the cleanup and removing the shortcut, all is working. The visual behavior is not critical, but you will see it if you set that Preference to Off. For some reason, when I reinstalled, Dropbox still knew my DB logon credentials and still logged in. Where were these stored?